Dissipation of Earthward Propagating Flux Rope Through Re‐reconnection with Geomagnetic Field: An MMS Case Study

Abstract

Three‐dimensional global hybrid simulations and observations have shown that earthward‐moving flux ropes (FRs) can undergo magnetic reconnection (or re‐reconnection) with the near‐Earth dipole field to create dipolarization front (DF)‐like signatures that are immediately preceded by brief intervals of negative BZ. The simultaneous erosion of the southward BZ field at the leading edge of the FR and continuous reconnection of lobe magnetic flux at the X‐line tailward of the FR result in the asymmetric south‐north BZ signature in many earthward‐moving FRs and possibly DFs with negative BZ dips prior to their observation. In this study, we analyzed Magnetospheric MultiScale (MMS) observation of fields and plasma signatures associated with the encounter of an ion diffusion region ahead of an earthward‐moving FR on 3 August 2017. The signatures of this re‐reconnection event were (i) +/− BZ reversal, (ii) −/+ bipolar‐type quadrupolar Hall magnetic fields, (iii) northward super‐Alfvénic electron outflow jet of ~1,000–1,500 km/s, (iv) Hall electric field of ~15 mV/m, (v) intense currents of ~40–100 nA/m2, and (vi) J·E′ ~0.11 nW/m3. Our analysis suggests that the MMS spacecraft encounters the ion and electron diffusion regions but misses the X‐line. Our results are in good agreement with particle‐in‐cell simulations of Lu et al. (2016, https://doi.org/10.1002/2016JA022815). We computed a dimensionless reconnection rate of ~0.09 for this re‐reconnection event and through modeling, estimating that the FR would fully dissipate by −16.58 RE. We demonstrated pertubations in the high‐latitude ionospheric currents at the same time of the dissipation of earthward‐moving FRs using ground‐ and space‐based measurements.

Asymmetric Reconnection Within a Flux Rope‐Type Dipolarization Front

“…The magnetic pressure and tension are largely balanced at the low-beta core of the flux rope . The possibility of this type of event was later confirmed with global hybrid simulations by Lu et al (2015) and has since been observed in other studies (Breuillard et al, 2016;Man et al, 2018;Poh et al, 2019). The plasmoid-type FRs form in the cross-tail current sheet on open field lines during multiple X-line reconnection and are carried tailward by fast exhaust flows from these X-lines (Baker et al, 1996;Slavin, Lepping, et al, 2003).…”

Comparative Analysis of the Vlasiator Simulations and MMS Observations of Multiple X‐Line Reconnection and Flux Transfer Events

“…For instance, during the coalescence process, the smaller island will be eroded by the larger of the two merging islands. Similar processes are also reported in the magnetotail wherein an earthward moving flux rope is eroded when interacting with the geomagnetic field (e.g., Lu et al, 2015;Man et al, 2018;Poh et al, 2019).…”

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

“…In spacecraft observations, flux ropes are often identified from bipolar variations in one magnetic field component and enhancement of magnetic strength at the center. There are various observations of flux ropes in the magnetosphere (e.g., Khurana et al 1995;Slavin 2003;Yang et al 2014;Sun et al 2019;Poh et al 2019), boundary of magnetosphere (e.g., Rijnbeek et al 1984;Kawano & Russell 1997;Fear et al 2008Fear et al , 2009Akhavan-Tafti et al 2018;Hwang et al 2018;Yao et al 2020), and solar wind (e.g., Zheng & Hu 2018;BlancoCano et al 2019;Bai et al 2020). Flux ropes are also observed in magnetospheres of Mercury (Zhong et al 2020a), Mars (Briggs et al 2011), Jupiter (Sarkango et al 2021), and Saturn (Jasinski et al 2016).…”

“…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). The flux ropes can change in size while moving through convection, often expanding (Dong et al 2017;Akhavan-Tafti et al 2018 and sometimes contracting (Hasegawa et al 2016).…”