A Volumetric Study of Flux Transfer Events at the Dayside Magnetopause

Abstract

Localized magnetic reconnection at the dayside magnetopause leads to the production of Flux Transfer Events (FTEs). The magnetic fields within the FTEs exhibit complex helical flux-rope topologies. Leveraging the adaptive mesh refinement strategy, we perform a three-dimensional magnetohydrodynamic simulation of the magnetosphere of an Earth-like planet and study the evolution of these FTEs. For the first time, we detect and track the FTE structures in 3D and present a complete volumetric picture of FTE evolution. The temporal evolutions of thermodynamic quantities within the FTE volumes confirm that continuous reconnection is indeed the dominant cause of active FTE growth, as indicated by the deviation of the pressure–volume curves from an adiabatic profile. An investigation into the magnetic properties of the FTEs shows a rapid decrease in the perpendicular currents within the FTE volume, exhibiting the tendency of internal currents toward being field-aligned. An assessment of the validity of the linear force-free flux-rope model for such FTEs shows that the structures drift toward a constant-α state but continuous reconnection inhibits the attainment of a purely linear force-free configuration. Additionally, the fluxes enclosed by the selected FTEs are computed to range between 0.3 and 1.5 MWb. The FTE with the highest flux content constitutes ∼1% of the net dayside open flux. These flux values are further compared against the estimates provided by the linear force-free flux-rope model. For the selected FTEs, the linear force-free model underestimated the flux content by up to 40%, owing to the continuous reconnected flux injection.

Global‐MHD Simulations Using MagPIE: Impact of Flux Transfer Events on the Ionosphere

“…The FTEs appear as helical flux ropes, displaying the characteristic features of patchy, multiple X‐line reconnection at the dayside magnetopause. These manifestations are similar to the FTEs observed in our previous resistive global‐MHD simulation using the PLUTO code (Paul et al., 2022). In the following sections, we focus our attention on two such FTEs, namely FTE‐1 and FTE‐2.…”

“…It has been established that the FTEs impinging on the polar cusp can cause localized reconnection between the FTE flux‐rope field lines and the cusp field lines owing to the favorable local topology of the magnetic field (Omidi & Sibeck, 2007). FACs are generated within FTEs as they evolve (Crooker & Siscoe, 1990; Paul et al., 2022; Saunders et al., 1984). Upon cusp‐FTE reconnection, these FACs can be chaneled along the newly reconnected field lines deeper into the cusp.…”

“…We now aim to analyze these signatures that are exhibited by the ionospheric surface in further detail. For the FTEs analyzed, we first identify the flux rope from its B N component at the magnetopause surface which appears as a bipolar patch (Paul et al., 2022). Thereafter, we locate the general region on the northern and southern cusp where the FTEs impinge on and trace the magnetic field lines from that region back to the ionospheric surface.…”

“…The physical effect of the diffusion coefficient is to broaden the magnetopause current layer (Komar, 2015). The above choice of the diffusion coefficient ensures that the magnetopause current sheet is consistently resolved by at least 7–8 grid cells (Paul et al., 2022). Additionally, this choice of the magnitude of the diffusion coefficient is also partially motivated by the fact that it sets the Lundquist number of the magnetopause current sheet at ∼6.7 × 10 4 (measured over a meridional slice with the Alfvén speed averaged over the magnetosheath and the magnetospheric values) which is larger than the threshold of occurrence of fast magnetic reconnection (Bhattacharjee et al., 2009).…”

“…The core model has been developed by Paul et al. (2022) using the resistive‐MHD module of the open source astrophysical gasdynamics code PLUTO (Mignone et al., 2007). An additional ionospheric module has been added in the current work.…”