A study of lightning flash initiation prior to the first initial breakdown pulse

© 2018 The Authors This study examines the initiation of two intracloud (IC) and two cloud-to-ground (CG) lightning flashes using electric field change (FA) sensors and VHF (LogRF) sensors located at seven sites near Oxford, Mississippi, USA. For each flash the initiating event caused a pulse in the LogRF data and started an Initial E-Change (IEC) in the FA data. The initiating LogRF pulses had powers ~1 μs. Numerous LogRF pulses occurred during each IEC; these pulses had durations ≤3 μs. Fewer FA pulses occurred during each IEC; these pulses had durations of ≤7 μs. During each IEC, a few of the LogRF pulses were coincident with a FA pulse, and most such pairs of pulses enhanced the IEC; no IEC enhancing events occurred without such a coincident pair. Each flash had 1 or 2 IEC enhancing events soon after the initiating event and 1 or 2 enhancing events shortly before the first classic initial breakdown (IB) pulse occurred. The point dipole moments and durations of IECs of the two IC flashes were (–520C m, 620 μs) and (–770C m, 1790 μs) and for the two CG flashes were (9C m, 124 μs) and (36C m, 130 μs). We speculate that the LogRF events were positive corona streamers, that enhancing events occurred when a new streamer extended a previous streamer path, and that this process during the flash initiation developed a nascent channel needed for the negative breakdown of the IB pulses

New WMO certified megaflash lightning extremes for flash distance (768 km) and duration (17.01 seconds) recorded from space

Initial global extremes in lightning duration and horizontal distance were established in 2017 (Lang et al. 2017) by an international panel of atmospheric lightning scientists and engineers assembled by the WMO. The subsequent launch of NOAA’s latest GOES-16/17 satellites with their Geostationary Lightning Mappers (GLMs) enabled extreme lightning to be monitored continuously over the western hemisphere up to 55° latitude for the first time. As a result, the former lightning extremes were more than doubled in 2019 to 709 km for distance and 16.730 s for duration (Peterson et al. 2020). Continued detection and analysis of lightning “megaflashes” (Sequin, 2021) has now revealed two flashes that even exceed those 2019 records. As part of the ongoing work of the WMO in detection and documentation of global weather extremes (e.g., El Fadli et al. 2013; Merlone et al. 2010), an international WMO evaluation committee was created to critically adjudicate these two GLM megaflash cases as new records for extreme lightning.We thank S. A. Rutledge and two other reviewers for their valuable comments. M. J. Peterson was supported by the U.S. Department of Energy through the Los Alamos National Laboratory (LANL) Laboratory Directed Research and Development (LDRD) program under project number 20200529ECR. Los Alamos National Laboratory is operated by Triad National Security, LLC, for the National Nuclear Security Administration of U.S. Department of Energy (Contract 89233218CNA000001). T. Logan supported by a NOAA Grant NA16OAR4320115 “Lightning Mapper Array Operation in Oklahoma and the Texas Gulf Coast Region to Aid Preparation for the GOES-R GLM.” I. Kolmasova was supported by GACR Grant 20-09671. S. D. Zhang was supported by a NOAA Grant NNH19ZDA001N-ESROGSS. The participation of J. Montanya in this work is supported by research Grant ESP2017-86263-C4-2-R funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe,” by the “European Union”; and Grants PID2019-109269RB-C42 funded by MCIN/AEI/10.13039/501100011033.Peer ReviewedPostprint (author's final draft

The Comet Interceptor Mission

Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA’s F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum ΔV capability of 600 ms−1. Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes – B1, provided by the Japanese space agency, JAXA, and B2 – that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission’s science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule

Observation of lightning-induced signals on the summit of La Grande Montagne: HF measurements

A ground-based version of the IME-HF analyzer, developed for the French TARANIS mission, was connected to a magnetic loop antenna and used for broadband measurements of lightning-induced signals in the frequency range from 5 kHz to 36 MHz. A sampling frequency of 80 MHz allows examining submicrosecond timing properties of recorded horizontal magnetic-field waveforms related to different lightning phenomena. The instrumentation is placed in a quiet electromagnetic environment of an external measurement site of the Laboratoire Souterrain à Bas Bruit (LSBB) on the summit of La Grande Montagne (1028 m, 43.94N, 5.48E). We present results of measurements recorded during two years of operation. We concentrate our attention on signals radiated by in-cloud processes which are difficult to detect in situ or optically. We also analyze a fine structure of the magnetic-field waveforms from different types of return strokes in order to investigate currents flowing in the lightning channels. After the launch of the TARANIS satellite the ground-based measurements will complement the observations from space

Evaluating the influence of lightning generated whistlers on the overall VLF wave intensity detected by a low-altitude spacecraft

International audienceThe influence of lightning generated whistlers on the overall very low frequency (VLF) wave intensity in the Earth's inner magnetosphere is still a subject of discussion. We combine lightning location data and VLF wave intensity measured by a low altitude spacecraft to identify frequency-location intervals where this influence is significant. The World Wide Lightning Location Network (WWLLN) provides a unique data set of times and locations of lightning strokes all around the world. When combined with the wave measurements performed by the DEMETER spacecraft (Sun-synchronous polar orbit, altitude of about 700 km), it allows us to calculate average/median power spectral densities of electric field fluctuations in the frequency range up to 20 kHz distinguished according to the lightning activity level. A comparison of the dependencies obtained for low and high lightning activity levels is then used to determine the influence of lightning generated whistlers. The obtained results are discussed in the frame of a possible relation to the plasmaspheric hiss generation

Evaluating the influence of lightning generated whistlers on the overall VLF wave intensity detected by a low-altitude spacecraft

International audienceThe influence of lightning generated whistlers on the overall very low frequency (VLF) wave intensity in the Earth's inner magnetosphere is still a subject of discussion. We combine lightning location data and VLF wave intensity measured by a low altitude spacecraft to identify frequency-location intervals where this influence is significant. The World Wide Lightning Location Network (WWLLN) provides a unique data set of times and locations of lightning strokes all around the world. When combined with the wave measurements performed by the DEMETER spacecraft (Sun-synchronous polar orbit, altitude of about 700 km), it allows us to calculate average/median power spectral densities of electric field fluctuations in the frequency range up to 20 kHz distinguished according to the lightning activity level. A comparison of the dependencies obtained for low and high lightning activity levels is then used to determine the influence of lightning generated whistlers. The obtained results are discussed in the frame of a possible relation to the plasmaspheric hiss generation

Eleven years of Cluster observations of whistler-mode chorus

International audienceElectromagnetic emissions of whistler-mode chorus carry enough power to increase electron fluxes in the outer Van Allen radiation belt at time scales on the order of one day. However, the ability of these waves to efficiently interact with relativistic electrons is controlled by the wave propagation directions and time-frequency structure. Eleven years of measurements of the STAFF-SA and WBD instruments onboard the Cluster spacecraft are systematically analyzed in order to determine the probability density functions of propagation directions of chorus as a function of geomagnetic latitude, magnetic local time, L* parameter, and frequency. A large database of banded whistler-mode emissions and time-frequency structured chorus has been used for this analysis. This work has received EU support through the FP7-Space grant agreement no 284520 for the MAARBLE collaborative research project

Whistler-mode waves and electromagnetic ion cyclotron waves in plasmaspheric plumes

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Propagation of lower-band whistler-mode waves in the outer Van Allen belt: Systematic analysis of 11 years of multi-component data from the Cluster spacecraft

International audienceLower-band whistler-mode emissions can influence the dynamics of the outer Van Allen radiation belts. We use 11 years of measurements of the STAFF-SA instruments onboard the four Cluster spacecraft to systematically build maps of wave propagation parameters as a function of position. We determine probability distributions of wave vector angle weighted by the wave intensity. The results show that wave vector directions of intense waves are close to a Gaussian-shaped peak centered on the local magnetic field line. The width of this peak is between 10 and 20 degrees. The cumulative percentage of oblique waves is below 1015%. This result is especially significant for an important class of whistler-mode emissions of lower-band chorus at higher latitudes, well outside their source region, where a simple ray tracing model fails and another mechanism is necessary to keep the wave vectors close to the field-aligned direction

Enhanced whistler occurrence rates close to VLF transmitters

International audienceGround-based military very low frequency (VLF) transmitters produce strong narrowband emissions. These propagate in the Earth-ionosphere waveguide and eventually penetrate through the ionosphere and propagate to larger radial distances. Significant ionospheric perturbations can be induced during the process, and, additionally, energetic electrons at a given L-shell can be precipitated due to their interaction with the transmitter signals. The plasma wave environment around the transmitter locations might thus be different than elsewhere. We use electromagnetic wave measurements performed by the DEMETER spacecraft to investigate this phenomenon. The neural network onboard DEMETER allows us to identify individual lightning whistlers observed by the spacecraft and to analyze their occurrence rates as a function of the distance from a VLF transmitter. We show that while for some transmitters lightning whistler occurrence rates peak close to the transmitter locations, for some transmitters no such effect is observed. We discuss this in terms of different transmitter frequencies and locations. We also investigate the significance of lightning whistler dispersion and local time