Global evolution of flux transfer events along the magnetopause from the dayside to the far tail

Abstract. Magnetic flux ropes are structures of magnetic field rolled-up along a longitudinal axis, which are forming in a variety of magnetised plasmas. In near-Earth space, flux ropes are a manifestation of energy transfer at the magnetopause and in the magnetotail current sheet. We present a new method to detect magnetic flux ropes in large-scale simulations, using only magnetic field line tracing. The method does not require prior identification of structures of interest such as current sheets or null lines, and thus allows one to identify flux ropes of any size and orientation, anywhere in the simulation domain. In this work, the new method is implemented in the hybrid-Vlasov model Vlasiator and demonstrated in global simulations of the terrestrial magnetosphere.

We study the evolution of flux ropes forming during flux transfer events on the dayside magnetopause under southward interplanetary magnetic field. It is found that flux ropes with an axial orientation along the dawn-dusk direction and propagating beyond the cusps will rapidly reconnect with the lobe magnetic field and vanish. In contrast, the flux ropes remaining near the equatorial plane and with an axial orientation along the flow direction, that is tangential to the magnetopause, can maintain their structure and propagate tens of Earth radii down the tail in the absence of a reconnecting shear magnetic field component. These results are a step forward in the global characterisation of flux ropes in and around the magnetosphere, and may help in guiding the search for elusive far-tail flux ropes in satellite measurements.