The Geometrical Features of Magnetic Flux Entanglement Events Observed by MMS

Abstract

Flux transfer events are momentary occurrences of self-adjusting, rope-like magnetized plasma structures near Earth's magnetopause, typically associated with a southward interplanetary magnetic field direction. This study aims to investigate the magnetic structural characteristics during three phases (initial, intermediate and final) of magnetic flux entanglement events and explore magnetic field gradient properties. Using the Nonlinear Magnetic Field Gradient Algorithm (NMG), we computed magnetic field curvature, helix angle, and torsion. Our analysis revealed that the central current sheet consistently exhibits the highest magnetic field curvature throughout all phases, while the lowest curvature occurs elsewhere. Notably, a polarity reversal in the normal component of magnetic field curvature is observed during the intermediate phase. The helix angle exhibits its maximum variation on both sides of the central current sheet during the initial phase. In the intermediate phase, however, the variation of the helix angle around the current sheet is minimal. By the final phase, the magnitude of the helix angle behaves in a manner opposite to that of the initial phase. Torsion around the current sheet initially undergoes significant changes during the initial phase but remains close to zero afterward. Conversely, in the intermediate phase, the magnetic flux regime shows minimal torsion initially, followed by an abrupt variations afterward. Nonetheless, during final phase, the magnetic flux regimes display a consistent pattern of increasing and decreasing torsion similar to the initial phase. In summary, flux tubes precede the emergence of flux ropes in the initial phase, structures resembling flux ropes dominate the intermediate phase, and both coexist in the final phase. This investigation sheds light on the interconnected nature of these structures, critical for understanding particle and energy exchange between the magnetosphere and solar wind.