Abstract

Flux transfer events are transient magnetized plasma structures that are self-balancing, rope-like phenomena that can appear at the Earth's magnetopause when the interplanetary magnetic field is southward. The formation of this type of flux rope has been unclear. Using measurements of particles and magnetic fields on the MMS spacecraft, we find that rope-like structures containing magnetospheric energetic electrons have exactly the same occurrence rate as those without magnetospheric electrons, independent of solar wind properties and location of observation. This equality is consistent with a pair of flux ropes being generated at the same time as an outcome of magnetic flux pileup reconnection. One resulting flux rope has its two ends connected to the magnetosphere, and the other is connected on both ends to the shocked solar wind.