Tailward flowing energetic oxygen ion bursts associated with multiple flux ropes in the distant magnetotail: GEOTAIL observations

An event of tailward flowing energetic (144 - 7959 keV) oxygen ion bursts was observed in the distant magnetotail (X = -63, Y = +7, Z = -3.8 R(E)) on February 13, 1994. The observations were made with the HEP-LD spectrometer oil board the GEOTAIL spacecraft. The event was associated with magnetic field signatures characteristic of multiple flux ropes. During the event, which lasted from 1847 to 1907 UT, strong impulsive increases in the oxygen flux were observed. From 1846 to 1900 UT the proton counting rate also exhibited an increase, followed by a decrease until the end of the oxygen event. The oxygen flux was confined to a rather narrow range in polar and azimuthal angle (only 7 - 10% of 4 pi was occupied). This implies a streaming distribution or beam-like structure. Comparison of the particle flow angles with the polar and azimuthal angles of the magnetic field indicates that the ion beam may have been embedded in flux ropes, which may be connecting the polar ionosphere and the distant magnetotail. During the observed oxygen event the ratio N-O/N-H+ is significantly higher than the ratios usually found in the center of the distant magnetotail. There is some evidence that the observed oxygen ions were more efficiently accelerated in this event than hydrogen and helium ions.Geosciences, MultidisciplinarySCI(E)27ARTICLE233267-32702

Electron Mirror-mode Structure: Magnetospheric Multiscale Observations

The small-scale mirror mode excited by electron dynamics is a fundamental physical process, attracting research interest in space, laboratory, and astrophysical plasma physics over the past half century. However, the investigations of this process were mostly limited to theories and numerical simulations, with no direct observational evidence for their existence. In this study we present clear observations of electron mirror-mode using Magnetospheric Multiscale data at unprecedented high temporal cadence. These structures are train-like, compressible, nonpropagating, and satisfy the theoretical excitation and electron trapping conditions. They were observed near the Earth's foreshock and its downstream turbulence during the corotating interaction region events, which could be involved with the interaction between solar wind and Earth

Electron energization and energy dissipation in microscale electromagnetic environments

Particle energization and energy dissipation in electromagnetic environments are longstanding topics of intensive research in space, laboratory, and astrophysical plasmas. One challenge is to understand these conversion processes at smaller and smaller spatial/temporal scales. In this Letter, with very high cadence measurements of particle distributions from the Magnetospheric Multiscale spacecraft, we report evidence of evolution of an identified microscale (i.e., electron gyro-scale) magnetic cavity structure and reveal within it a unique energization process that does not adhere to prevailing adiabatic invariance theory. Our finding indicates that this process is largely energy dependent, and can accelerate/decelerate charged particles inside the trapping region during their gyromotion, clearly altering the particle distribution