ALBERT

Beschreibung: Kinetic wave-particle interactions in Earth’s outer radiation belt energize and scatter high-energy electrons, playing an important role in the dynamic variation of the extent and intensity of the outer belt. It is possible to model the effects of wave-particle interactions across long length and time scales using quasi-linear theory, leading to a Fokker-Planck equation to describe the effects of the waves on the high energy electrons. This powerful theory renders the efficacy of the wave-particle interaction in a diffusion coefficient that varies with energy or momentum and pitch angle. In this article we determine how the Fokker-Planck equation responds to the temporal variation of the quasi-linear diffusion coefficient in the case of pitch-angle diffusion due to plasmaspheric hiss. Guided by in-situ observations of how hiss wave activity and local number density change in time, we use stochastic parameterisation to describe the temporal evolution of hiss diffusion coefficients in ensemble numerical experiments. These experiments are informed by observations from three different example locations in near-Earth space, and a comparison of the results indicates that local differences in the distribution of diffusion coefficients can result in material differences to the ensemble solutions. We demonstrate that ensemble solutions of the Fokker-Planck equation depend both upon the timescale of variability (varied between minutes and hours), and the shape of the distribution of diffusion coefficients. Based upon theoretical construction of the diffusion coefficients and the results presented here, we argue that there is a useful maximum averaging timescale that should be used to construct a diffusion coefficient from observations, and that this timescale is likely less than the orbital period of most inner magnetospheric missions. We discuss time and length scales of wave-particle interactions relative to the drift velocity of high-energy electrons and confirm that arithmetic drift-averaging is can be appropriate in some cases. We show that in some locations, rare but large values of the diffusion coefficient occur during periods of relatively low number density. Ensemble solutions are sensitive to the presence of these rare values, supporting the need for accurate cold plasma density models in radiation belt descriptions.

Beschreibung: The Earth’s magnetic field traps charged particles which are transported longitudinally around Earth, generating a near-circular current, known as the ring current. While the ring current has been measured on the ground and space for many decades, the enhancement of the ring current during geomagnetic storms is still not well understood, due to many processes contributing to its dynamics on different time scales. Here, we show that existing ring current models systematically overestimate electron flux observations of 10–50 keV on the nightside during storm onset. By analyzing electron drift trajectories, we show that this systematic overestimation of flux can be explained through a missing loss process which operates in the pre-midnight sector. Quantifying this loss reveals that the theoretical upper limit of loss has to be reached over a broad region of space in order to reproduce the observations. This missing loss may be attributed to inaccuracies in the parameterization of the loss due to chorus wave interactions, combined with the scattering by electrostatic electron cyclotron harmonic waves which is currently not included in ring current models.

Beschreibung: 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.

Beschreibung: Ring current particles, which are heavily influenced by geomagnetic activity, excite plasmawaves (e.g., EMIC, chorus etc) and affect the terrestrial magnetospheric configuration, which modifies particle trajectories. During geomagnetic storms, specifically the recovery phase, the ring current becomes disturbed and decays via various loss processes (e.g., charge exchange, Coulomb collisions, and EMIC wave scattering). These disturbances in the ring current contribute significantly to the development of the Dst index. Since the ring current plays a crucial role in magnetospheric dynamics through its spatial and temporal evolution, understanding how it impacts the Dst index remains an ongoing topic of research.In this study, we present the first simulation results of the ring current using the Versatile near-Earth environment of Radiation Belts and ring current - 4D (VERB-4D) code, peviously known as the Versatile Electron Radiation Belt - 4D code. Our simulations are compared to the Van Allen Probes HOPE and RBSPICE during a geomagnetic storm on March 17, 2013. We study the evolution of the MLT-resolved and average Dst index during the storm‘s recovery phase while examining the relative contributions of charge exchange, Coulomb drag, and radial diffusion.

Beschreibung: There have been a number of theories proposed concerning the loss of relativistic electrons from the radiation belts. However, direct observations of loss were not possible on a number of previous missions due to the large field of view of the instruments and often high-altitude orbits of satellites that did not allow researchers to isolate the precipitating electrons from the stably trapped. We use measurements from the ELFIN-L suit of instruments flown on Lomonosov spacecraft at LEO orbit, which allows us to distinguish stably trapped from the drift loss cone electrons. The sun-synchronous orbit of Lomonosov allows us to quantify scattering that occurred into the loss cone on the dawn-side and the dusk-side magnetosphere. The loss at MeV energies is observed predominantly on the dawn-side, consistent with the loss induced by the chorus waves. The companion data publication provides processed measurements.

Beschreibung: The fundamental processes responsible for energy exchange between large-scale electromagnetic fields and plasma are well understood theoretically, but in practice these theories have not been tested. These processes are ubiquitous in all plasmas, especially at the interface between high and low beta plasmas in planetary magnetospheres and other magnetic environments. Although such boundaries pervade the plasma Universe, the processes responsible for the release of the stored magnetic and thermal plasma energy have not been fully identified and the importance of the relative impact of each process is unknown. Despite advances in understanding energy release through the conversion of magnetic to kinetic energy in magnetic reconnection, how the extreme pressures in the regions between stretched and more relaxed field lines in the transition region are balanced and released through adiabatic convection of plasma and fields is still a mystery. Recent theoretical advances and the predictions of large-scale instabilities must be tested. In essence, the processes responsible remain poorly understood and the problem unresolved. The aim of the White Paper submitted to ESA’s Voyage 2050 call, and the contents of this paper, is to highlight three outstanding open science questions that are of clear international interest: (i) the interplay of local and global plasma physics processes: (ii) the partitioning during energy conversion between electromagnetic and plasma energy: and (iii) what processes drive the coupling between low and high beta plasmas. We present a discussion of the new measurements and technological advances required from current state-of-the-art, and several candidate mission profiles with which these international high-priority science goals could be significantly advanced.

Beschreibung: This study presents a systematic analysis of ion flow, and accompanying electric and magnetic fields, from the Space Weather Modeling Framework (SWMF). Inside of 10 R_E the flow speeds are typically under 50 km/s during quiet and moderate driving conditions, but fast flows well in excess of 100 km/s regularly develop during the main phase of storm intervals. In particular, a strong sunward flow is seen in the simulation results, at various places in the near-Earth tail region and near the terminator plane, between 5 and 12 R_E. These regions (extending from the nightside around both dawn and dusk flanks) can have persistent flows over 200 km/s, confined near the equatorial plane and with local electric fields in excess of 10 mV/m. They seem to be fairly persistent and exist in regions of low plasma pressure; the inclusion or exclusion of an inner magnetospheric drift physics model does not significantly alter there timing, location, or intensity. As the driving diminishes, so do these fast flows. The field lines are clearly not electric equipotentials during these intervals, with a peak electric field at the equatorial plane (rather than the ionosphere, as equipotential mapping would dictate). The features and physics of these fast flows are presented and discussed. Comparisons are made against flow and field measurements from various spacecraft, like the Van Allen Probes, GOES, THEMIS, and MMS, showing that, occasionally, signatures like this flow feature exist in the data, but not on such a regular basis as in the code results.

Beschreibung: Here, we present an empirical model of the equatorial electron pitch angle distributions, based on the Magnetic Electron Ion Spectrometer (MagEIS) instrument aboard the Van Allen Probes. The model was created for energies from 37 keV up to 2.65 MeV. The model uses the solar wind dynamic pressure as a driving parameter and has a continuous dependence on Lm, magnetic local time and activity. It works for L-shells from 3.05 up around 5.95. For each channel of the MagEIS instrument, there are two files with model coefficients, one for Pdyn 〈5.5-6 nPa (e.g., “Pijk_246_keV.dat’) , and the second one for very high dynamic pressure values above 5.5 nPa (e.g., “Pijk_246_keV_HIGH.dat’). The script to read both file types is provided (“read_coefs.py”), and the data format is explained in the readme file.

Beschreibung: A distinct population of ultrarelativistic electrons has been observed in the outer radiation belt after several geomagnetic storms, and recent modeling results indicate that an existing seed population, and depletions in plasmasphere electron density, are a necessary condition for the appearance of this electron population. In order to similarly deepen our understanding of the solar wind drivers behind the appearance of these electrons with extreme energy, we catalog storms corresponding to ultrarelativistic enhancements by origin, and begin to establish necessary and sufficient solar wind conditions for these enhancement events. To do so, we perform superposed epoch analysis on a 6 year period from 2012 to 2018, using solar wind data from the Omniweb service, as well as electron flux and electron density data products from the Van Allen Probes mission. We also consider connections to wave-particle interactions by including a chorus wave proxy in the analysis, and provide an overview of further modeling objectives and open questions for continued investigation of this electron population.