Abstract
AbstractWe utilized 33 years of data obtained by the Geotail, THEMIS, Cluster and MMS missions to investigate the slow (<200 km/s) ion flows perpendicular to the magnetic field in Earth's magnetotail plasma sheet. By using plasma β as a proxy of distance to the neutral sheet, we find that the ion flow patterns vary systematically within the plasma sheet. Particularly, in regions farther from the neutral sheet, earthward (tailward) flows exhibit a strong tendency to diverge (converge) quasi‐symmetrically, with respect to the midnight meridional plane. As the distance becomes closer toward the neutral sheet, this tendency to diverge and converge gradually weakens. Moreover, duskward flows become the dominant components in both the earthward and tailward flows. These variations in ion flow patterns with distance to neutral sheet are hemispherically independent. We suggest that the spatial profiles of the electric and diamagnetic drift vary with distance to the neutral sheet and are therefore responsible for the varying ion flow patterns.
Highlights
The Earth's magnetotail plasma sheet plays an important role in governing the energy, mass and momentum transport in the coupled magnetosphere-ionosphere system
Observation (2): duskward flows become the dominant components. We suggest that these characteristic variations are likely due to the variations in the distribution of the electric (VE) and diamagnetic drift (Vdia) with distance to the neutral sheet
By using plasma β as a proxy of distance to the neutral sheet, we find that the ion flow patterns vary systematically within the plasma sheet
Summary
The Earth's magnetotail plasma sheet plays an important role in governing the energy, mass and momentum transport in the coupled magnetosphere-ionosphere system. Previous studies have primarily focused on (a.) fast and slow flows (Angelopoulos et al, 1994, 1992; Baumjohann et al, 1990; Juusola, Østgaard, & Tanskanen, 2011; Raj et al, 2002; Zhang, Wang, et al, 2015), (b.) perpendicular and field-aligned flows (Baumjohann et al, 1988; Decoster & Frank, 1979; Raj et al, 2002; Takahashi & Hones, 1988), (c.) earthward and tailward flows (Juusola, Østgaard, & Tanskanen, 2011; Zhang, Baumjohann, et al, 2015; Ohtani et al, 2009; Schödel, Nakamura, et al, 2001), (d.) distant-tail and near-Earth flows (Ohtani et al, 2009; Schödel, Baumjohann, et al, 2001; Nakamura et al, 1994), as well as (e.) the dependence on external environments, for instance, on the orientation of the interplanetary magnetic field (Pitkänen et al, 2019; Wang et al, 2006), and on substorms and steady magnetospheric convection (Juusola, Østgaard, Tanskanen, Partamies, & Snekvik, 2011; McPherron et al, 2011) These studies point toward that the plasma behaviors in the different regions within the plasma sheet can vary significantly under various environments. By utilizing 0.5 as a lower limit of plasma β (ratio of ion thermal pressure to magnetic pressure) in identifying the CHONG ET AL
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