Abstract
Abstract. We use a test particle model to explore anisotropy and fast flows in the central plasma sheet (CPS) that are a consequence of plasma sheet boundary layer (PSBL) ion beam dynamics. Ion distributions and flows (velocity moments) in the CPS and equatorial current sheet (CS) are compared and we find that mirroring of initially earthward beams from the PSBL, and their subsequent convection to the CS region, results in strong anisotropy throughout the CPS. At higher latitudes, velocity moments are field-aligned and feature earthward flow. Deeper in the CPS, velocity moments yield flows in the anti-earthward direction. There is no clear distinction between the PSBL and CPS, since velocity distributions with large streaming components occur throughout the model CPS, but in the CS region they are anisotropic and nongyrotropic. In the CS region velocity moments can feature anti-earthward cross field flows. These tailward flows (> 400 km/s) are observed in the CS region between X = - 20 to - 30 RE due to nonadiabatic effects. Model results suggest that fast tailward plasma flows can be obtained without necessarily appealing to magnetotail processes associated with dynamic geomagnetic activity.Key words. Magnetospheric physics (magnetospheric con-figuration and dynamics) – Space plasma physics (charge particle motion and acceleration; numerical simulation studies)
Highlights
While, to the first order, the plasma sheet (PS) comprises a warm ion population with bulk flows primarily dominated by large scale E × B convection, careful inspection of distribution functions reveals many anisotropic flows encompassing a wide range of time scales
In the plasma sheet boundary layer (PSBL) the flows are nearly field-aligned, whereas in the central plasma sheet (CPS) and near the current sheet (CS) region about 70% of the fast flows are predominantly perpendicular to the magnetic field direction (Baker et al, 1996)
It is believed that in the CPS much of the fast plasma transport is across field lines rather than along them
Summary
To the first order, the plasma sheet (PS) comprises a warm ion population with bulk flows primarily dominated by large scale E × B convection, careful inspection of distribution functions reveals many anisotropic flows encompassing a wide range of time scales. In the PSBL the flows are nearly field-aligned, whereas in the CPS and near the current sheet (CS) region about 70% of the fast flows are predominantly perpendicular to the magnetic field direction (Baker et al, 1996). Lyons et al (1999, 2000) found evidence that the flows within the CPS and those within the PSBL may not be distinct phenomena They found that when they are observed, significant flows appear to exist throughout the entire height of the tail plasma sheet, and are associated with structured currents in the tail. Bursty flows could be associated with some flapping motion of the magnetotail in the Z-direction This is different from the standard picture, and means that bursty flows in the current sheet region might be present regardless of the presence or absence of an acceleration mechanism, such as a neutral line. We compare the ion distributions and flows (velocity moments) in the CPS and equatorial CS
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