Transient and localized processes in the magnetotail: a review

Many phenomena in the Earth's magnetotail have characteristic temporal scales of several minutes and spatial scales of a few Earth radii (<I>R<sub>E</sub></I>). Examples of such transient and localized mesoscale phenomena are bursty bulk flows, beamlets, energy dispersed ion beams, flux ropes, traveling compression regions, night-side flux transfer events, and rapid flappings of the current sheet. Although most of these observations are linked to specific interpretations or theoretical models they are inter-related and can be the different aspects of a physical process or origin. Recognizing the inter-connected nature of the different transient and localized phenomena in the magnetotail, this paper reviews their observations by highlighting their important characteristics, with emphasis on the new results from Cluster multipoint observations. The multi-point Cluster measurements have provided, for the first time, the ability to distinguish between temporal and spatial variations, and to resolve spatial structures. Some examples of the new results are: flux ropes with widths of 0.3 <I>R<sub>E</sub></I>, transient field aligned currents associated with bursty bulk flows and connected to the Hall current at the magnetic reconnection, flappings of the magnetotail current sheet with time scales of 100 s–10 min and thickness of few thousand km, and particle energization including velocity and time dispersed ion structures with the latter having durations of 1–3 min. The current theories of these transient and localized processes are based largely on magnetic reconnection, although the important role of the interchange and other plasma modes are now well recognized. On the kinetic scale, the energization of particles takes place near the magnetic X-point by non-adiabatic processes and wave-particle interactions. The theory, modeling and simulations of the plasma and field signatures are reviewed and the links among the different observational concepts and the theoretical frameworks are discussed. The mesoscale processes in the magnetotail and the strong coupling among them are crucial in developing a comprehensive understanding of the multiscale phenomena of the magnetosphere

Neonatal developmental venous anomalies: Clinicoradiologic characterization and follow-up

BACKGROUND AND PURPOSE: Although developmental venous anomalies have been frequently studied in adults and occasionally in children, data regarding these entities are scarce in neonates. We aimed to characterize clinical and neuroimaging features of neonatal developmental venous anomalies and to evaluate any association between MR imaging abnormalities in their drainage territory and corresponding angioarchitectural features. MATERIALS AND METHODS: We reviewed parenchymal abnormalities and angioarchitectural features of 41 neonates with developmental venous anomalies (20 males; mean corrected age, 39.9 weeks) selected through a radiology report text search from 2135 neonates who underwent brain MR imaging between 2008 and 2019. Fetal and longitudinal MR images were also reviewed. Neurologic outcomes were collected. Statistics were performed using x 2, Fisher exact, Mann-Whitney U, or t tests corrected for multiple comparisons. RESULTS: Developmental venous anomalies were detected in 1.9% of neonatal scans. These were complicated by parenchymal/ventricular abnormalities in 15/41 cases (36.6%), improving at last follow-up in 8/10 (80%), with normal neurologic outcome in 9/14 (64.2%). Multiple collectors (P =.008) and larger collector caliber (P <.001) were significantly more frequent in complicated developmental venous anomalies. At a patient level, multiplicity (P =.002) was significantly associated with the presence of ≥1 complicated developmental venous anomaly. Retrospective fetal detection was possible in 3/11 subjects (27.2%). CONCLUSIONS: One-third of neonatal developmental venous anomalies may be complicated by parenchymal abnormalities, especially with multiple and larger collectors. Neuroimaging and neurologic outcomes were favorable in most cases, suggesting a benign, self-limited nature of these vascular anomalies. A congenital origin could be confirmed in one-quarter of cases with available fetal MR imaging

Modeling of Magnetic Dipolarizations and Turbulence in Earth’s Magnetotail as Factors of Plasma Acceleration and Transfer

The paper is devoted to studying processes of plasma particle acceleration in the process of magnetic dipolarizations in a current sheet of Earth’s magnetotail. A numerical model is constructed that allows evaluation of particle acceleration in three possible scenarios: (A) Proper dipolarization; (B) Passage of multiple dipolarization fronts; (C) Passage of fronts followed by high-frequency electromagnetic oscillations. The energy spectra of three types of accelerated particles are obtained: hydrogen H+ and oxygen O+ ions and electrons e–. It is shown that, at different time scales, predominant acceleration of various particle populations occurs in scenarios (A)–(C). Oxygen ions are accelerated most efficiently in single dipolarization process (A), protons (and, to some extent, electrons), in scenario (B), whereas scenario (C) is most efficient for acceleration of electrons. It is shown that accounting for high-frequency electromagnetic fluctuations, accompanying magnetic dipolarization, may explain the appearance of streams of particles with energies on the order of hundreds of keV in Earth’s magnetotail