Abstract
AbstractFast earthward plasma flows are commonly observed in the magnetotail plasma sheet. These flows are often termed as bursty bulk flows because of their bursty nature, and they are considered to be generated by magnetic reconnection. Close to the neutral sheet (Bx ∼ 0), the fast flows are considered to be associated with an enhanced dawn‐to‐dusk electric field (Ey > 0), which together with the northward magnetic field component (Bz > 0) protrude the plasma earthward via enhanced E × B‐drift. Sometimes, reversals in the dawn‐dusk velocity component perpendicular to the magnetic field (V⊥y) are measured in association with Bx sign changes in the flows. This suggests that the electric field component in the north‐south direction (Ez) can play a role in determining the dawn‐dusk direction of the enhanced drift. We present data measured by the Magnetospheric Multiscale, which demonstrate that Ez can have a dictating role for V⊥y of fast flows. Furthermore, it is shown that the critical contribution of Ez is not limited only to V⊥y, but it can also dominantly determine the enhanced drift of the fast flows in the X direction (V⊥x). The latter can occur also near and at the neutral sheet, which adds an alternative configuration to the conventional picture of Ey and Bz being the main players in driving the earthward fast flows. The domination of Ez in the studied events appears with potential signatures of an influence of a nonzero dawn‐dusk component of the interplanetary magnetic field (IMF By) on the magnetotail.
Highlights
The magnetotail plasma sheet is commonly accommodated by intermittent earthward high-speed ion bulk flows, often termed as fast flows, flow bursts, or bursty bulk flows (BBFs) (Angelopoulos et al, 1992, 1994; Baumjohann et al, 1990; Cao et al, 2006; Raj et al, 2002)
The latter can occur near and at the neutral sheet, which adds an alternative configuration to the conventional picture of Ey and Bz being the main players in driving the earthward fast flows
We investigate the ion drift in fast flow events measured by the Magnetosphere Multiscale (MMS) mission showing clear V⊥y reversals, and the relative importance of different EiBj-terms in determining V⊥x and V⊥y according to Equation 1
Summary
The magnetotail plasma sheet is commonly accommodated by intermittent earthward high-speed ion bulk flows, often termed as fast flows, flow bursts, or bursty bulk flows (BBFs) (Angelopoulos et al, 1992, 1994; Baumjohann et al, 1990; Cao et al, 2006; Raj et al, 2002) These longitudinally localized high-speed flows with speeds ranging from ∼100 to ∼1,000 km/s are considered to be generated by magnetic reconnection. We investigate the ion drift in fast flow events measured by the Magnetosphere Multiscale (MMS) mission showing clear V⊥y reversals, and the relative importance of different EiBj-terms (where i and j go through x, y, and z) in determining V⊥x and V⊥y according to Equation 1.
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