Based on observations from the Magnetospheric Multiscale mission, this study presents an analysis of a short large-amplitude magnetic structures (SLAMS) event with simultaneous occurrence of low- and high-frequency magnetosonic whistler waves. It was found that low-frequency magnetosonic whistler waves around the lower-hybrid frequency emerge in the presence of solar wind ions and local low-energy ions in the trailing region of SLAMS. Additionally, counter-propagating whistler waves (the high-frequency branch of the magnetosonic whistler wave) are observed within SLAMS, coinciding with a perpendicular temperature anisotropy in the electron population. Instability analyses demonstrate that these low-frequency waves are induced by the two-stream instability associated with the cross-field drift of low-energy ions relative to electrons, while whistler waves are locally generated by the whistler anisotropy instability. Our results shed light on the impact of SLAMS on particle and wave dynamics in the terrestrial foreshock.

We directly estimate the in situ current density of the Earth’s ring current (RC) using the curlometer method and investigate its morphology using the small spatial separations and high accuracy of the Magnetospheric Multiscale mission (MMS). Through statistical analysis of data from September 2015 to the end of 2016, covering the region of 2-8 RE (Earth radius, 6371 km), we reveal an almost complete near-equatorial (within ) RC morphology in terms of radial distance and local time (MLT) which complements and extends that found from previous studies. We found no evidence of RC enhancement on the dusk-side during geomagnetic active periods, but details of local time (MLT) asymmetries in, and the boundary between, the inner (eastward) and outer (westward) currents are revealed. We propose that part of the asymmetry demonstrated here suggests that in addition to the overall persistence of the westward RC, two large banana-like currents are directly observed, one which could arise from a peak of plasma pressure near ~4.8 RE on the noon side and the other from a valley of plasma pressure which could arise near ~4.8 RE on the night side.

In this study, a novel algorithm for jointly estimating the linear and quadratic gradients of physical quantities with multiple spacecraft observations based on the least square method has been put forward for the first time. With 10 or more spacecraft constellation measurements as the input, this new algorithm can yield both the linear and quadratic gradients at the barycenter of the constellation. Iterations have been used in the algorithm. The tests on cylindrical flux ropes, dipole magnetic field and modeled geo-magnetospheric field have been carried out. The tests indicate that the linear gradient gained has the second order accuracy, while the quadratic gradient is of the first order accuracy. The test on the modeled geo-magnetospheric field shows that, the more the number of the spacecraft in the constellation, the high the accuracy of the quadratic gradient calculated. However, the accuracy of the linear gradient yielded is independent of the number of the spacecraft. The feasibility, reliability and accuracy of this algorithm have been verified successfully. This algorithm can find wide applications in the design of the future multiple S/C missions as well as in the analysis of multiple point measurement data.

The data from the CLUSTER FGM magnetometer, recorded for 20 years at ESA’s Cluster Science Archive, have been used to form a database aligned in time. It allows the calculation of curl(B) over all the life of the mission. The ̵⃗B and J⃗ data are then averaged, as a function of the dipole tilt angle, to form a 3D grid of spatial extend of 20 RE, and for any spatial resolution. From these data grids, maps of the direction of the magnetic field and of the current density are produced, allowing the observation of the average behavior of the magnetic field and the current density on a large scale. The validity of the calculation of J⃗ is discussed. By means of spatial interpolation, the grids are used to provide a measurement of the magnetic field at any point in space where the grid is filled. This allows possibility of ray tracing to obtain empirical plots of the magnetic field lines, i.e. not theoreti-cal, but from experimental data. Field lines near the cusp are visualized, even if they are very smoothed by the averaging of IMF and solar wind parameters. In a future work it would be possible to add other classification than just the dipole tilt angle, such as various activity indicese and solar wind parameters. The prospect of adding data from other missions would extend the regions that have been covered by Cluster, and in-crease the spatial extent of the 3D grid and its resolution.

Topological configurations of the magnetic field play key roles in the evolution of space plasmas. This paper presents a novel algorithm that can estimate the quadratic magnetic gradient as well as the complete geometrical features of magnetic field lines, based on magnetic field and current density measurements by a multiple spacecraft constellation at 4 or more points. The explicit estimators for the linear and quadratic gradients, the apparent velocity of the magnetic structure and the curvature and torsion of the magnetic field lines can be obtained with well predicted accuracies. The feasibility and accuracy of the method have been verified with thorough tests. The algorithm has been successfully applied to exhibit the geometrical structure of a flux rope. This algorithm has wide applications for uncovering a variety of magnetic configurations in space plasmas.

This White Paper outlines the importance of addressing the fundamental science theme “How are charged particles energized in space plasmas” through a future ESA mission. The White Paper presents five compelling science questions related to particle energization by shocks, reconnection, waves and turbulence, jets and their combinations. Answering these questions requires resolving scale coupling, nonlinearity, and nonstationarity, which cannot be done with existing multi-point observations. In situ measurements from a multi-point, multi-scale L-class Plasma Observatory consisting of at least seven spacecraft covering fluid, ion, and electron scales are needed. The Plasma Observatory will enable a paradigm shift in our comprehension of particle energization and space plasma physics in general, with a very important impact on solar and astrophysical plasmas. It will be the next logical step following Cluster, THEMIS, and MMS for the very large and active European space plasmas community. Being one of the cornerstone missions of the future ESA Voyage 2050 science programme, it would further strengthen the European scientific and technical leadership in this important field.