A possible source mechanism for magnetotail current sheet flapping

Abstract

<jats:p>Abstract. The origin of the flapping motions of the current sheet in the Earth's magnetotail is one of the most interesting questions of magnetospheric dynamics yet to be solved. We have used a polar plane simulation from the global hybrid-Vlasov model Vlasiator to study the characteristics and source of current sheet flapping in the center of the magnetotail. The characteristics of the simulated signatures agree with observations reported in the literature. The flapping is initiated by a hemispherically asymmetric magnetopause perturbation, created by subsolar magnetopause reconnection, that is capable of displacing the tail current sheet from its nominal position. The current sheet displacement propagates downtail at the same pace as the driving magnetopause perturbation. The initial current sheet displacement launches a standing magnetosonic wave within the tail resonance cavity. The travel time of the wave within the local cavity determines the period of the subsequent flapping signatures. Compression of the tail lobes due to added flux affects the cross-sectional width of the resonance cavity as well as the magnetosonic speed within the cavity. These in turn modify the wave travel time and flapping period. The compression of the resonance cavity may also provide additional energy to the standing wave, which may lead to strengthening of the flapping signature. It may be possible that the suggested mechanism could act as a source of kink-like waves that have been observed to be emitted from the center of the tail and to propagate toward the dawn and dusk flanks. </jats:p>

Hybrid-Vlasov modelling of nightside auroral proton precipitation during southward interplanetary magnetic field conditions

“…This simulation run was previously used in several studies focusing on various phenomena and regions in the near-Earth space, such as dayside magnetopause reconnection (Hoilijoki et al, 2017), ion acceleration in the magnetosheath (Jarvinen et al, 2018), magnetotail reconnection (Palmroth et al, 2017;Juusola et al, 2018a), and magnetotail current sheet flapping (Juusola et al, 2018b). In each of these studies, the presented results showed good correspondence with earlier findings.…”

Solar Wind Directional Change Triggering Flapping Motions of the Current Sheet: MMS Observations

“…Recently, simulation results show that subsolar magnetopause reconnections can create hemispherically asymmetric magnetopause perturbations, which initiate flapping motions (Juusola et al, 2018). Magnetosonic waves are expected to be launched within the local tail, which can be regarded as a cavity, and their travel time within the cavity determines the period of the flapping (Juusola et al, 2018). As a comparison, the periods of the flapping in Figure 3 are almost the same with the variations of V Z, SW , indicating that another mechanism could contribute to the generation of this flapping.…”

“…Flapping motions can be generated by external sources (Shen et al, 2008) as well as internal sources (Malova et al, 2007;Wei et al, 2015). Recently, simulation results show that subsolar magnetopause reconnections can create hemispherically asymmetric magnetopause perturbations, which initiate flapping motions (Juusola et al, 2018). Magnetosonic waves are expected to be launched within the local tail, which can be regarded as a cavity, and their travel time within the cavity determines the period of the flapping (Juusola et al, 2018).…”

“…Several candidate mechanisms have been proposed to explain the generation of flapping motions, such as the asymmetric ion flow in the Northern and Southern Hemispheres of the tail (Malova et al, 2007), excitation of the magnetic double gradient instability (Erkaev et al, 2008;Korovinskiy et al, 2013), nonadiabatic ions (Wei et al, 2015), instabilities associated with ion temperature anisotropy (Wu et al, 2016), the enhancement of the solar wind velocity (Shen et al, 2008), and hemispherically asymmetric magnetopause perturbations (Juusola et al, 2018).…”

Large‐Amplitude Oscillatory Motion of Mercury's Cross‐Tail Current Sheet

“…Observational studies at Earth (Forsyth et al, 2009;Sun et al, 2014) demonstrated that the magnetic double-gradient instability model best describes the observational data. Other observational (Forsyth et al, 2009;Shen et al, 2008) and numerical (Juusola et al, 2018;Sergeev et al, 2008) studies had also proposed solar wind variations as an external source for the excitation of flapping waves within Earth's magnetotail.…”