Temporal Evolution of Flux Tube Entanglement at the Magnetopause as Observed by the MMS Satellites

Abstract

Flux transfer events (FTEs), as flux ropes (FRs), are considered key agents for solar wind energy to enter the terrestrial magnetosphere. Recent observations identify entangled flux tubes that collide and pull against each other. Reconnection occurs to disentangle and produce a new pair of FRs with different connectivity. In this paper, we examine the entanglement interface and how such an entanglement process evolves in time by comparing 17 entanglements observed by the Magnetospheric Multiscale (MMS) mission. The B y-dominated interplanetary magnetic field (IMF) distribution of the 17 events agrees with previous findings. We have identified three evolutionary stages characterized by the magnetic field and pressure enhancement. Our study confirms the FR nature of these events and explains how a disparate pair of ropes is formed from two entangled flux tubes, each initially connected to a different hemisphere of the magnetosphere. Plain Language Summary The Earth's intrinsic magnetic field deflects the solar wind flow at a boundary called the magnetopause. Near this boundary, twisted flux tubes are found. Such tubes may become entangled if they move toward each other, say, from the Southern and Northern Hemispheres. This study analyzes 17 such events and identifies three evolutionary stages as the entanglement proceeds. The results improve our understanding of not only the complex coupling between solar wind and the Earth's magnetic field but other similar processes in space plasma.

Temporal Evolution of Flux Rope/Tube Entanglement in 3‐D Hall MHD Simulations

“…Later at T = 20 and 30 min, as is plotted in 3‐D in Figures 3 and 4, and observed by Qi et al. (2020), the field lines, instead of curving toward the individual flux rope axes, do curve toward the central current sheet, consistent with the picture that the two ropes are actively pulling against each other.…”

“…In contrast, events found in MMS observations consist of compression on both sides with a current sheet in the middle. This configuration is consistent with two magnetic flux tubes merging at their interface (Øieroset et al., 2019; Qi et al., 2020).…”

“…Compared with the three stages identified by Qi et al. (2020), our T = 10 min is an early stage, between T = 20 and 30 min is the middle stage, and between T = 30 and 40 min represents the late stage evolving into disconnected tubes.…”

“…The originally disparate flux tubes then collide and merge, producing a pair of flux tubes with axis approximately perpendicular to each other (entanglement), via a second round of magnetic reconnection (Russell & Qi, 2020). Following this hypothesis, multiple cases consistent with the early, middle, and late stages of time evolution of such FTE reconnections have been identified in the MMS data obtained between 2015 and 2018 (Qi et al., 2020).…”

Kinetic-scale flux ropes: Observations and applications of kinetic equilibrium models

“…Recent simulations show that reconnection can generate not only fluid-scale flux ropes but also those with ion-or even electron-scales (Daughton et al 2011;Hoilijoki et al 2019;Lu et al 2020). These kinetic-scale flux ropes may interact with one another to form larger-scale flux ropes (Daughton et al 2011), which could be manifested in spacecraft observations as entangled flux ropes (Wang et al 2017;Øieroset et al 2019;Qi et al 2020). There are also observations of ion-scale flux ropes near the ion/electron diffusion region (Wang et al 2016;Hwang et al 2018;Poh et al 2019;Dong et al 2020).…”