Description: Measurements of electromagnetic waves in space plasmas are an important tool for our understanding of physical processes in this environment. Inter-calibration of data from different spacecraft missions is necessary for combining their measurements in empirical models or case studies. We show results collected during a close conjunction of the Van Allen Probes and Arase spacecraft. The inter-calibration is based on a fortuitous case of common observations of strong whistlers at frequencies between a few hundred hertz and 10 kHz, which are generated by the same lightning strokes and which propagate along very similar paths to the two spacecraft. Measured amplitudes of the magnetic field fluctuations are the same within ∼14% precision of our analysis, corresponding to 1.2 dB. Currently, archived electric field measurements show twice larger amplitudes on Arase compared to Van Allen Probes but they start to match within ∼33% precision (2.5 dB) once the newest results on the interface of the antennas to the surrounding plasma are included in the calibration procedures. Ray tracing simulations help us to build a consistent scenario of wave propagation to both spacecraft reflected by a successful inter-calibration of the polarization and propagation parameters obtained from multicomponent measurements. We succeed in linking the spacecraft observations to localizations of lightning return strokes by two different ground-based networks which independently verify the correctness of the Universal Time tags of waveform measurements by both spacecraft missions, with an uncertainty better than 10 ms.

Description: We conduct test particle simulations to study the perturbations in a hot electron velocity distribution caused by a rising chorus element propagating parallel to the ambient magnetic field in the Earth's outer radiation belt. The wavefield is constructed from the nonlinear growth theory of chorus emissions of Omura (2021, https://doi.org/10.1186/s40623-021-01380-w), with additional considerations about saturation and propagation of the transverse resonant current being applied to model the subpacket structure. Using Liouville's theorem, we trace electrons back in time to reconstruct the evolution of electron velocity distribution at the magnetic equator. The electromagnetic hole created by nonlinear trapping and transport effects appears as a depression in the velocity distribution, aligned with the resonance velocity curve. We analyze the decrease of particle flux in this depression and estimate the energy resolution, pitch angle resolution, time resolution and geometric factor of particle analyzers needed to observe the perturbation. We conclude that particle detectors on current or recently operating spacecraft are always lacking in at least one of these parameters, which explains the missing direct observations of sharp phase space density depressions during chorus-electron nonlinear resonant interaction. However, with a dedicated experiment and appropriate measurement strategy, such observations are within the possibilities of the current technology. Similarity of the simulated density perturbation and a step function mathematical model is used to draw an analogy between the backward wave oscillator regime of chorus generation and the nonlinear growth theory.

Description: The STRATELEC (STRatéole-2 ATmospheric ELECtricity) project, funded by CNES, focuses on the deployment of new atmospheric electricity instrumentation on-board several Stratéole-2 stratospheric balloons. The STRATELEC project aims at i) Documenting the electrical state of the atmosphere and the production of high-energy radiation for better understanding and modeling of the processes induced by thunderstorms through opportunity flights within the Stratéole-2 mission; ii) Identifying state-of-the-art technologies to build the STRATELEC instrumentation package with new sensors in the perspective for implantation on stratospheric balloons, high-altitude aircraft, and even low-altitude drones; iii) Contributing to additional scientific returns on any space mission dedicated to lightning detection and more generally to the study of electrodynamic couplings in the terrestrial atmosphere-ionosphere-magnetosphere system. Five technical tasks are currently underway : 1) identifying the technologies needed to address the scientific objectives of the project and their Technology Readiness Level ; 2) assessing the requirements and mitigation plans to install the identified technologies on Stratéole-2 platforms for a deployment during the last Stratéole-2 campaign during winter 2025-2026 ; 3) developing, testing and operating STRATELEC instrumentation ; 4) assessing the probability of tropical convective clouds within Stratéole-2 flight domain ; and 5) characterizing the lightning activity along Stratéole-2 flights. An overview of the STRATELEC scientific and technical objectives and the list of targeted observations will be first presented. The current status of the different technical tasks will be then discussed with a focus on the analysis of the lightning activity in the West Hemisphere as recorded during the first Stratéole-2 flights.

Description: The PAGER project provides space weather predictions that are initiated from observations on the Sun and predicts radiation in space and its effects on satellite infrastructure. Real-time predictions and a historical record of the dynamics of the cold plasma density and ring current allow for evaluation of surface charging, and predictions of the relativistic electron fluxes allow for the evaluation of deep dielectric charging. The project provides a 1-2 day probabilistic forecast of ring current and radiation belt environments, which will allow satellite operators to respond to predictions that present a significant threat. As a backbone of the project, we use the most advanced codes that currently exist and adapt existing codes to perform ensemble simulations and uncertainty quantifications. This project includes a number of innovative tools including data assimilation and uncertainty quantification, new models of near-Earth electromagnetic wave environment, ensemble predictions of solar wind parameters at L 1, and data-driven forecast of the geomangetic Kp index and plasma density. Our developed codes may be used in the future for realistic modelling of extreme space weather events. The PAGER consortium is made up of leading academic and industry experts in space weather research, space physics, empirical data modelling, and space environment effects on spacecraft from Europe and the US.

Description: FARBES (Forecast of Radiation Belt Scenarios) is a recently started H2020 project to predict the subsequent behavior of a geomagnetic storm after its arrival. For such predictions, FARBES intends to use only ground-based, real-time data to produce input parameters of the radiation belt model, like Salammbô. These input parameters are 1. Outer boundary (magnetopause boundary and injected distribution from the plasmasheet); 2. Background plasma density; 3. Amplitudes of natural waves and their distribution (Chorus, Hiss, EMIC, lightning-whistlers); 4. Amplitude and distribution of radial diffusion coefficients; 5. The low energy boundary condition. Here we focus on the third input data, the ‘Amplitudes of natural waves and their distribution.’ To get the specifications of the in situ natural wave environment, we created an empirical transfer function to describe the attenuation/amplification of whistler-mode waves during their quasi-parallel propagation from the equator through the ionosphere to the ground. We used whistler-mode waves from satellites, like Van Allen Probes, Cluster, and DEMETER, and the ground-based VLF recordings of AWDANet. For this study, we selected the 0.1-0.9 fce (giro-frequency) frequency range of the spectrograms to calculate the average wave powers. Ground-based spectrograms required extensive noise removal (sferics, hum harmonics, etc.) considering the daily attenuation variation of the Earth-Ionosphere waveguide.