Investigation of storm time magnetotail and ion injection using three‐dimensional global hybrid simulation

Abstract

2014), Investigation of storm time magnetotail and ion injection using three-dimensional global hybrid simulation, Abstract Dynamics of the near-Earth magnetotail associated with substorms during a period of extended southward interplanetary magnetic field is studied using a three-dimensional (3-D) global hybrid simulation model that includes both the dayside and nightside magnetosphere, for the first time, with physics from the ion kinetic to the global Alfvénic convection scales. It is found that the dayside reconnection leads to the penetration of the dawn-dusk electric field through the magnetopause and thus a thinning of the plasma sheet, followed by the magnetotail reconnection with 3-D, multiple flux ropes. Ion kinetic physics is found to play important roles in the magnetotail dynamics, which leads to the following results: (1) Hall electric fields in the thin current layer cause a systematic dawnward ion drift motion and thus a dawn-dusk asymmetry of the plasma sheet with a higher (lower) density on the dawnside (duskside). Correspondingly, more reconnection occurs on the duskside. Bidirectional fast ions are generated due to acceleration in reconnection, and more high-speed earthward flow injections are found on the duskside than the dawnside. Such finding of the dawn-dusk asymmetry is consistent with recent satellite observations. (2) The injected ions undergo the magnetic gradient and curvature drift in the dipole-like field, forming a ring current. (3) Ion particle distributions reveal multiple populations/beams at various distances in the tail. (4) Dipolarization of the tail magnetic field takes place due to the pileup of the injected magnetic fluxes and thermal pressure of injected ions, where the fast earthward flow is stopped. Oscillation of the dipolarization front is developed at the fast-flow braking, predominantly on the dawnside. (5) Kinetic compressional wave turbulence is present around the dipolarization front. The cross-tail currents break into small-scale structures with k ⟂ i ∼ 1, where k ⟂ is the perpendicular wave number. A sharp dip of magnetic field strength is seen just in front of the sharp rise of the magnetic field at the dipolarization front, mainly on the duskside. (6) A shear flow-type instability is found on the duskside flank of the ring current plasma, whereas a kinetic ballooning instability appears on the dawnside. (7) Shear Alfvén waves and compressional waves are generated from the tail reconnection, and they evolve into kinetic Alfvén waves in the dipole-like field region. Correspondingly, multiple field-aligned current filaments are generated above the auroral ionosphere.Geomagnetic substorms are one of the most important global-scale dynamic processes in the magnetosphere. Through the substorm, solar wind energy transmitted from the dayside magnetopause can be released from the magnetotail and injected into the high-latitude ionosphere. Since storms/substorms are conducive to strong particle injections from the tail plasma sheet and variations in the electromagneti...

Tail reconnection in the global magnetospheric context: Vlasiator first results

“…Using a local two-fluid simulation of the current sheet, Ohtani et al (2004) shows multiple X points, of which one starts to dominate after reconnection spreads to the lobe field lines. Similar conclusions are made based on local kinetic simulations (Lapenta et al, 2015) and by global hybrid-PIC simulations (Lin et al, 2014). The earthward-moving multiple reconnection sites have been observed by, e.g., Eastwood et al (2005) using the Cluster spacecraft.…”

“…Since the simulation is still 2-D at the moment, our results concern reconnection in a single meridional plane and cannot be generalised to concern multiple reconnection sites on a global 3-D current layer. Using a much coarser resolution, Lin et al (2014) found multiple X lines but that dominant X lines can form if they are not competing with other X lines on a similar meridional plane. Future versions of Vlasiator shall investigate whether this is also true in the hybrid-Vlasov approach.…”

“…More sophisticated plasma descriptions, like the fully and partially kinetic approaches, have been applied in local geometries (e.g. Zeiler et al, 2002;Lapenta et al, 2015) and also recently in global setups (Lin et al, 2014(Lin et al, , 2017Lu et al, 2015). In the local simulations studying tail reconnection, tail reconnection needs to be initiated artificially by an additional perturbation, which may not correctly represent the driving of tail reconnection by reconnected magnetic flux from the dayside.…”

Ion motion in a polarized current sheet

“…This may explain why spacecraft observations in Earth's magnetotail have shown electron currents to be much stronger than ion currents 6,39,54 . Similar results are found in numerical simulations 28,29 . An electric field E z can play an essential role in ion energization within thin current sheets located near the reconnection region.…”

Evolution of flux ropes in the magnetotail: A three-dimensional global hybrid simulation

“…In our previous study, 44 we investigated several important processes associated with substorms such as dipolarization, ballooning instability, and ion injection. In the present study, we mainly focus on the physics of the flux ropes and magnetotail reconnection.…”