Transient and localized processes in the magnetotail: a review

Abstract

Abstract. Many phenomena in the Earth's magnetotail have characteristic temporal scales of several minutes and spatial scales of a few Earth radii (R E ). 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 R E , 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 Correspondence to: A. S. Sharma (ssh@astro.umd.edu) 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.

Formation of current density profile in tilted current sheets

“…Alternatively, during a slip-type deformation, the flux tubes shift vertically relative to their neighbors, but the magnetic field orientation remains the same, irrespective of the normal direction and the sheet tilt. Quiet-time stronglytilted sheets, forming a significant subset of Cluster flapping events, were consistent with a slip-type displacement (see also Sharma et al, 2008). A good example is the 3 August 2004 event (Fig.…”

Uv Transient Brightenings Associated With a Coronal Mass Ejection

“…The filamentary nature of CSs has been predicted theoretically by Lee & Fu (1985) and Lee (1995) and confirmed by CLUSTER observations in the magnetotail (e.g., Slavin et al 2003Slavin et al , 2005Eastwood et al 2005): plasmoids observed by CLUSTER well fit a scenario of multiple X-lines where reconnection takes place and produces plasmoids. Observations have also shown that one of the many X-lines, for so far unknown reasons, becomes dominant (Sharma et al 2008).…”

Current sheet flapping in the near-Earth magnetotail: peculiarities of propagation and parallel currents

“…However, other manifestations of CS dynamics (e.g. earthward plasma flows with dipolarisation fronts, formation of plasmoids) are also observed (Sharma et al, 2008;Baumjohann et al, 2007). One can distinguish two kinds of flapping motion: the vertical oscillations of the quasi-horizontal CSs (when the normal N to the CS plane is basically along the z axis, |N z | > 0.8, and kink-like waves do not propagate) and formation of tilted CSs (when the normal is significantly tilted, |N z | < 0.8, and kink-like waves can propagate along the dusk-dawn direction) (see details of this classification in Rong et al, 2015).…”