The scale of the magnetotail reconnecting current sheet in the presence of O⁺

Abstract

The reconnection current layer thickness is expected to scale with either the ion inertial length or the ion gyroradius. Both of these quantities scale with the mass of the ions present. During geomagnetically disturbed times, the reconnection layer in the magnetotail can contain a significant amount of O + . UsingCluster multi-spacecraft measurements, we have studied nine reconnection events in the magnetotail plasmasheet, to determine whether the reconnecting current sheet thickness scales with the ion gyroradius or the ion inertial length, and whether the amount of O + in the plasma sheet has an effect on the current layer thickness. We find that the thickness is equal to the H + gyroradius, even when the plasma sheet has a high O + content. This result is in contrast to Hall MHD expectations and likely results from the multiscale nature of the current sheet.

Current Sheets in the Earth Magnetotail: Plasma and Magnetic Field Structure with Cluster Project Observations

“…The increase of O + results in the increase of the CS thickness in agreement with modeling (Zelenyi et al 2006). This effect confirms kinetic nature of CS and can play the important role in CS stability (Shay and Swisdak 2004;Markidis et al 2011;Karimabadi et al 2011;Liu et al 2014).…”

Oxygen acceleration in magnetotail reconnection

“…Note that the current sheet thicknesses are the same for the three runs even though the oxygen concentration is different. The thickness of current sheet is independent of the oxygen contents as suggested in both of the theory of Harris current sheets (i.e., the current sheet thickness is determined by the ambient magnetic field, the plasma temperature, and the cross‐tail speed) [e.g., Galeev , ] and observations [e.g., Liu et al ., ]. Figure shows the DF profiles at the center of the current sheet.…”

“…Oxygen of ionospheric origin in the lobes flows into the plasma sheet and replaces the plasma sheet protons during the tearing instability in the magnetotail [ Karimabadi et al ., ]. Although there is no evidence that these oxygen ions change the thickness of the current sheet [ Liu et al ., ], as a heavy ion species the oxygen can influence magnetotail reconnection processes in several other ways, e.g., reducing the reconnection rate [e.g., Shay and Swisdak , ; Karimabadi et al ., ; Markidis et al ., ; Liang et al ., ], slowing down outflow speed and dipolarization front (DF) propagation speed [e.g., Liang et al ., ], generating “heavy whistler waves” that mediate the reconnection [ Shay and Swisdak , ], and forming multiscale diffusion regions [e.g., Liu et al ., ].…”

Coronal Heating Topology: The Interplay of Current Sheets and Magnetic Field Lines

“…It has become increasingly clear that the effective heating and particles acceleration occur at scales of the order of the ion (proton) inertial length d i (Sonnerup 1979;Mozer et al 2002;Phan et al 2007;Xiao et al 2007;Wu et al 2011;Liu et al 2014), that in the solar corona, for an ion density n i ∼ 10 8 cm −3 , is d i = c/ω pi ∼ 23 m (ω pi = 4πn i e 2 /m i is the proton plasma frequency, c the speed of light, e the electron charge, and m i the proton mass). For typical hot coronal loops with temperatures T ∼ 10 6 K and magnetic field intensities B ∼ 50 G the ion gyroradius is much smaller than d i (reaching d i only in the higher β regions typical of the solar wind).…”