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

Abstract

The Vlasiator hybrid‐Vlasov code was developed to investigate global magnetospheric dynamics at ion‐kinetic scales. Here we focus on the role of magnetic reconnection in the formation and evolution of magnetic islands at the low‐latitude magnetopause, under southward interplanetary magnetic field conditions. The simulation results indicate that (1) the magnetic reconnection ion kinetics, including the Earthward pointing Larmor electric field on the magnetospheric side of an X‐point and anisotropic ion distributions, are well‐captured by Vlasiator, thus enabling the study of reconnection‐driven magnetic island evolution processes, (2) magnetic islands evolve due to continuous reconnection at adjacent X‐points, “coalescence” which refers to the merging of neighboring islands to create a larger island, “erosion” during which an island loses magnetic flux due to reconnection, and “division” which involves the splitting of an island into smaller islands, and (3) continuous reconnection at adjacent X‐points is the dominant source of magnetic flux and plasma to the outer layers of magnetic islands resulting in cross‐sectional growth rates up to + 0.3 RE2/min. The simulation results are compared to the Magnetospheric Multiscale (MMS) measurements of a chain of ion‐scale flux transfer events (FTEs) sandwiched between two dominant X‐lines. The MMS measurements similarly reveal (1) anisotropic ion populations and (2) normalized reconnection rate ~0.18, in agreement with theory and the Vlasiator predictions. Based on the simulation results and the MMS measurements, it is estimated that the observed ion‐scale FTEs may grow Earth‐sized within ~10 min, which is comparable to the average transport time for FTEs formed in the subsolar region to the high‐latitude magnetopause. Future simulations shall revisit reconnection‐driven island evolution processes with improved spatial resolutions.

Cross‐Scale Quantification of Storm‐Time Dayside Magnetospheric Magnetic Flux Content

“…A large FTE was observed during the SSC phase, indicating the occurrence of dayside magnetic reconnection (e.g., Akhavan‐Tafti et al, 2020). The FTE contained nearly 160 MWb, much larger than other FTE observations (e.g., Wang et al, 2006).…”

“…Signatures of dayside magnetic flux erosion, that is, magnetic reconnection, and tailward flux transport were observed during the SSC phase. In particular, during the encounter with the ICME 2 sheath region, the MMS spacecraft detected reconnected magnetic flux at the magnetopause transported tailward as bundles of “open” magnetic flux tubes with a flux rope‐like geometry, known as flux transfer events (FTEs) (e.g., Akhavan‐Tafti, Slavin, Eastwood, et al, 2019; Akhavan‐Tafti, Slavin, Sun, et al, 2019; Akhavan‐Tafti et al, 2020; Russell & Elphic, 1979). Figure 7a shows the close‐up view of the magnetic signatures inside and surrounding the FTE in the turbulent magnetosheath behind the quasi‐parallel bow shock (e.g., Pollock et al, 2018).…”

Flux Transfer Events at a Reconnection‐Suppressed Magnetopause: Cassini Observations at Saturn

“…FTEs are also commonly observed and well-studied at Earth's magnetopause by a variety of spacecraft as well as in numerical simulations (e.g. Lockwood & Hapgood, 1998;Varsani et al, 2014;Eastwood et al, 2016;Akhavan-Tafti et al, 2020).…”

Vlasov simulation of electrons in the context of hybrid global models: an eVlasiator approach

“…As portions of our simulation domain have proton temperature up to 10 8 K, we use an empirical estimate of T i /T e ∼ 4 as magnetosheath temperature ratios are usually around 4 to 12 (Wang et al, 2012). Frank (1994), Hoshino et al (2001), Artemyev et al (2011), andGrigorenko et al (2016) show similar proton-electron temperature ratios in the magnetotail. In order to constrain the extent of our velocity space and numerical requirements of our solver, we implement our electrons with a mass of 10 times the true electron mass, resulting in an ion-to-electron mass ratio of m i /m e = 183.6.…”