A Volumetric Study of Flux Transfer Events at the Dayside Magnetopause

TL;DR

This study uses advanced 3D MHD simulations with AMR to analyze the volumetric evolution of flux transfer events at Earth's magnetopause, revealing insights into their magnetic structure, growth mechanisms, and flux content.

Contribution

It presents the first 3D detection and tracking of FTEs, providing a comprehensive volumetric analysis and evaluating the linear force-free flux rope model's applicability.

Findings

FTEs exhibit complex helical flux-rope topologies.

Continuous reconnection drives FTE growth and prevents linear force-free state.

FTE flux ranges from 0.3 to 1.5 MWb, with linear models underestimating flux by up to 40%.

Abstract

Localized magnetic reconnection at the dayside magnetopause leads to the production of Flux Transfer Events (FTEs). The magnetic field within the FTEs exhibit complex helical flux-rope topologies. Leveraging the Adaptive Mesh Refinement (AMR) strategy, we perform a 3-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 evolution 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 P-V curves from an adiabatic profile. An investigation into the magnetic properties of the FTEs show a rapid decrease in the perpendicular currents within the FTE volume exhibiting the tendency of internal currents toward being field aligned. An assessment on the validity of the linear force-free flux rope model for such FTEs show that the structures drift towards a constant-$\alpha$ state but continuous reconnection inhibits the attainment of a purely linear force-free configuration. Additionally, the flux enclosed by the selected FTEs are computed to range between 0.3-1.5 MWb. The FTE with the highest flux content constitutes $\sim$ 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.