Topology and signatures of a model for flux transfer events based on vortex‐induced reconnection

Abstract

A model of the disturbed magnetic field and disturbed velocity of flux transfer events (FTEs) is deduced on the basis of the vortex-induced reconnection theory. The topology and signatures of FTEs are calculated and discussed. We propose that the observed forms of FTE signatures depend on the motional direction of the FTE tube, the positions of the spacecraft relative to the passing FTE tube, and which part of the FTE tube (the magnetosphere part, the magnetopause part, or the magnetosheath part) the spacecraft is passing through. It is found that when a FTE tube moves from south to north along a straight line in the northern hemisphere, positive FTEs appear for most passages; however, reverse FTEs are also observed occasionally while the signatures of Bz (Boe) appear as a single peak, and the irregular FTEs always correspond to oblique line motions of the FTE tube. The velocity signatures are similar to those of the magnetic field, but in the northern hemisphere their directions are all just opposite to the magnetic field. The calculated results for the magnetic field are compared with 61 observed FTEs. The observed signatures (BN and Boe) of 52 FTEs are consistent with our calculations. The results indicate that a majority of observed FTEs correspond to passages of spacecraft through the edges of FTE tubes. 1.

Dual roles of shear flow in nonlinear multi-scale interactions

“…As illustrated in figure 5(c), on the other hand, the plasmas inside magnetic island rotate along with closed magnetic field lines around O-point, testifying the theoretical predication of vortex flow formation convincingly. In fact, we have to point out that similar phenomena of the island accompanyied with in-phase vortex have been already observed in the flux transfer event in space plasmas [3,34] as well as in toroidal helical discharges in magnetic fusion plasmas [35], although the relevant dual roles of shear flow have not been previously identified.…”

“…The findings reported can have potentially significant implications in astrophysical, space, and laboratory plasmas, since the phenomena of macro-scale magnetic islands accompanying with shear flow (or vortex) are often observed in a variety of plasma systems. In magnetospheric plasmas, vortex-induced magnetic reconnection can occur at the magnetopause in the presence of a velocity shear, which has been proposed to explain the formation of flux transfer event, one of the most important phenomenons observed by spacecraft and satellite [3,34]. In magnetic fusion plasmas (in particular, for advanced steady-state tokamak and stellerator, etc), self-generated zonal flow or imposed mean flow interacts with magnetic island strongly, and in fact the in-phase island and vortex have been already observed in the large helical device [35].…”

“…Shear flow has been widely accepted to play an essential role in stabilizing various instabilities and suppressing turbulent transport in astrophysical, space, and laboratory plasmas as well as neutral fluids [1][2][3][4]. Especially in the magnetic confinement fusion device, the transport quenching by shear flow is identified as a key mechanism for the formation of transport barriers, which are a unique feature for the high-confinement plasma regime [5][6][7][8].…”

On the cause of a magnetospheric flux transfer event

“…In addition, it has been very successful in both explaining and predicting observed ionospheric signatures in the cusp region (such as extended flow channels and cusp ion steps). the dependence of the occurrence on IMF Bz, the mixing of magnetosheath and magnetosphere plasma inside FTEs, and the field twist there [Liu et al, 1992;Shi et al, 1991]. However, it cannot explain the accelerated flows Seen on the trailing edge of some FTEs, as this flow is formed by the evolution of field lines away from a single reconnection site [Ma et al, 1994].…”

Initial results of high‐latitude magnetopause and low‐latitude flank flux transfer events from 3 years of Cluster observations

“…Since the discovery of FTEs [ Russell and Elphic , 1978, 1979; Haerendel et al , 1978], their statistical properties have been widely studied [e.g., Paschmann et al , 1982; Berchem and Russell , 1984; Rijnbeek et al , 1984; Southwood et al , 1986; Elphic , 1990; Kawano et al , 1992; Kuo et al , 1995; Kawano and Russell , 1996, 1997a; Sanny et al , 1996, 1998]. In addition to the original flux rope model proposed by Russell and Elphic [1978], several other FTE models have been proposed to explain the FTE formation based on large‐scale FTE statistical results [e.g., Lee and Fu , 1985; Scholer , 1988; Sibeck , 1990; Liu et al , 1992].…”