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Traditionally, it is widely assumed that the source of electron precipitation in the region of diffuse aurora is wave‐particle interaction processes in the Earth's plasmasheet. It is difficult to imagine that ionosphere‐thermosphere system is also actively involved in the formation of electron precipitation and provides a very noticeable energy contribution to this process. In this study, we use specifically designed simulation scenarios of the SuperThermal Electron Transport code to clearly distinguish between the magnetospheric and ionospheric contributions to the precipitating electrons in the region of diffuse aurora. It is demonstrated that atmospheric collisional processes and the overall magnetosphere‐ionosphere‐atmosphere energy circulation dynamics, with the participation of two magnetically conjugate hemispheres, play a very important role in the formation of electron energy fluxes that are coming from the magnetosphere. Plain Language Summary: It is widely agreed that the electrons originating in space are primarily responsible for the initiation of the beautiful light displays of aurora in the sky. This is definitely true, because the ignition of polar lights is driven by the different acceleration processes in near‐Earth space. These processes, however, do not provide the total amount of energy coming into the polar ionosphere‐thermosphere system carried by precipitating auroral electrons. As we find and explain in this letter, the atmosphere by itself, provides an additional and very noticeable amount of energy to the electrons driving the aurora. This energy is drawn from a reservoir built up by the interaction of electrons with magnetically connected portions of the atmosphere, which traps and redistributes the incoming energy. The result is that more energy can appear to be carried by precipitating electrons than is provided instantaneously by the acceleration processes in space. This substantial additional energy is only possible because of the interaction with the atmosphere. We demonstrate this phenomena using carefully designed numerical simulations. Key Points: Electron precipitation dynamics in the region of diffuse auroraDistinguishing between electrons of magnetospheric and ionospheric origins using SuperThermal Electron Transport code simulation scenariosThe quantitative assessment of the role of atmospheric collisions in electron precipitation phenomena in diffuse aurora [ABSTRACT FROM AUTHOR]

An intriguing aspect of the famous September 2, 1859 geomagnetic disturbance (or "Carrington" event) is the horizontal magnetic (BH) data set measured in Colaba, India (magnetic latitude approximately 20°N). The field exhibits a sharp decrease of over 1,600 nT and a quick recovery of about 1,300 nT, all within a few hours during the daytime. The mechanism behind this has previously been attributed to magnetospheric processes, ionospheric processes or a combination of both. In this study, we outline our efforts to replicate this low-latitude magnetic field using the Space Weather Modeling Framework. By simulating an extremely high pressure solar wind scenario, we can emulate the low- latitude surface magnetic signal at Colaba. In our simulation, magnetospheric currents adjacent to the near-Earth magnetopause and strong Region 1 field-aligned currents are the main contributors to the large Colaba BH. The rapid recovery of BH in our simulated scenario is due to the retreat of these magnetospheric currents as the magnetosphere expands, as opposed to ring current dynamics. In addition, we find that the scenario that best emulated the surface magnetic field observations during the Carrington event had a minimum calculated Dst value between -431 and -1,191 nT, indicating that Dst may not be a suitable estimate of storm intensity for this kind of event. [ABSTRACT FROM AUTHOR]

The electron precipitation in the region of the diffuse aurora should be considered as a two‐step process (Khazanov et al., 2017, https://doi.org/10.1002/2016GL072063). The first one is the interaction of plasma sheet electrons with electrostatic electron cyclotron and/or whistler waves, moving those electrons into the loss cone to precipitate in both magnetically conjugate atmospheres. The second step is the interaction of these electrons with the ionosphere and atmosphere via their elastic and nonelastic collisions and reflection (backscatter) of degraded electrons back to magnetosphere and conjugate ionospheres. This paper presents the results of a newly developed scenario of nonsteady‐state electron precipitation dynamics that accounts for magnetosphere‐ionosphere‐atmosphere energy interplay over the entire energy range of the plasma sheet electron population and their affiliated secondary electrons. It also studies how both magnetically conjugate auroral regions work together with the magnetosphere in the formation of electron precipitation in the region of the diffuse aurora with the energy range coverage from 1 eV up to 10 keV. Key Points: The electron precipitation in the region of the diffuse aurora should be considered as a two‐step processNewly developed scenario of nonsteady‐state electron precipitation dynamics is discussedAsymmetry and MI coupling play a role in the formation of low energy electron precipitation [ABSTRACT FROM AUTHOR]

On 27 June 1996, the NASA Galileo spacecraft made humanity’s first flyby of Jupiter’s largest moon, Ganymede, discovering that it is the only moon known to possess an internally generated magnetic field. Resurrecting the original Galileo Plasma Subsystem (PLS) data analysis software, we processed the raw PLS data from G01 and for the first time present the properties of plasmas encountered. Entry into the magnetosphere of Ganymede occurred near the confluence of the magnetopause and plasma sheet. Reconnection-driven plasma flows were observed (consistent with an Earth-like Dungey cycle), which may be a result of reconnection in the plasma sheet, magnetopause, or might be Ganymede’s equivalent of a Low-Latitude Boundary Layer. Dropouts in plasma density combined with velocity perturbations afterward suggest that Galileo briefly crossed the cusps into closed magnetic field lines. Galileo then crossed the cusps, where field-aligned precipitating ions were observed flowing down into the surface, at a location consistent with observations by the Hubble Space Telescope. The density of plasma outflowing from Ganymede jumped an order of magnitude around closest approach over the north polar cap. The abrupt increase may be a result of crossing the cusp or may represent an altitude-dependent boundary such as an ionopause. More diffuse, warmer field-aligned outflows were observed in the lobes. Fluxes of particles near the moon on the nightside were significantly lower than on the dayside, possibly resulting from a diurnal cycle of the ionosphere and/or neutral atmosphere. [ABSTRACT FROM AUTHOR]

During the 14 November 2012 geomagnetic storm, the Van Allen Probes spacecraft observed a number of sharp decreases (“dropouts”) in particle fluxes for ions and electrons of different energies. In this paper, we investigate the global magnetosphere dynamics and magnetosphere– ionosphere (M–I) coupling during the dropout events using multipoint measurements by Van Allen Probes, TWINS, and AMPERE together with the output of the two-way coupled global BATS-R-US–CRCM model. We find different behavior for two pairs of dropouts. For one pair, the same pattern was repeated: (1) weak nightside Region 1 and 2 Birkeland currents before and during the dropout; (2) intensification of Region 2 currents after the dropout; and (3) a particle injection detected by TWINS after the dropout. The model predicted similar behavior of Birkeland currents. TWINS low-altitude emissions demonstrated high variability during these intervals, indicating high geomagnetic activity in the near-Earth tail region. For the second pair of dropouts, the structure of both Birkeland currents and ENA emissions was relatively stable. The model also showed quasi-stationary behavior of Birkeland currents and simulated ENA emissions with gradual ring current buildup. We confirm that the first pair of dropouts was caused by large-scale motions of the OCB (open–closed boundary) during substorm activity. We show the new result that this OCB motion was associated with global changes in Birkeland (M–I coupling) currents and strong modulation of low-altitude ion precipitation. The second pair of dropouts is the result of smaller OCB disturbances not related to magnetospheric substorms. The local observations of the first pair of dropouts result from a global magnetospheric reconfiguration, which is manifested by ion injections and enhanced ion precipitation detected by TWINS and changes in the structure of Birkeland currents detected by AMPERE. This study demonstrates that multipoint measurements along with the global model results enable the reconstruction of a more complete system-level picture of the dropout events and provides insight into M–I coupling aspects that have not previously been investigated. [ABSTRACT FROM AUTHOR]

Spacecraft formation flying in co-planar identical orbits with oppositely directed apse lines (eccentricity vectors) allows simultaneous in-situ measurements in different altitudes and time-sequential measurements in a limited altitude range (rapid revisit); a key enabling factor in understanding many poorly understood phenomena in our atmosphere and its interaction with the magnetosphere. The dynamics and control problem for flying formations in mirrored orbits are investigated using the Mechanisms of Energetic Mass Ejection - Explorer (MEME-X) mission concept as a case study. It is determined that the proposed two-craft and four-craft configurations require routine maintenance to correct their relative motion. The formation maintenance costs are quantified for both configurations and determined to be within the capabilities of small satellites. A high-fidelity end-to-end simulation is developed to model the entire two-craft mission concept, from orbit insertion to decommissioning, providing an approximate baseline for the flight dynamics costs of similar missions using multiple spacecraft flying in mirrored orbits. • Spacecraft formation flying in mirrored orbits is investigated. • The dynamics and control of two-craft and four-craft geometries are explored. • The proposed formation-keeping strategies are verified for a novel mission concept. • The formation-keeping costs are quantified for both formation configurations. [ABSTRACT FROM AUTHOR]