Topology of magnetic flux ropes and formation of fossil flux transfer events and boundary layer plasmas

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Abstract
At the dayside magnetopause, magnetic flux ropes can form as a result of multiple X line reconnection. In this process the presence of at least two parallel X lines leads to the formation of a magnetic flux rope with each additional X line giving another flux rope. For a finite extent of these X lines the magnetic flux of the flux ropes is connected to the external magnetic field on one or the other side of the current layer. In general, such a flux rope has frayed ends, i.e., magnetic flux enters the rope from the magnetospheric as well as from the magnetosheath side and/or exits the rope to either side of the layer. However, it is shown that for an appropriate extent and location of two neighboring X lines, a simple magnetic topology can be expected, in which the major amount of magnetic flux of the rope is connected at each end to only one side of the current sheet. For a sufficient relative shift of the X lines, magnetic flux may enter a flux rope from the magnetosphere and exit into the magnetosphere. This process leads to the formation of magnetic flux ropes which contain a considerable amount of magnetosheath plasma on closed magnetospheric field lines. We discuss this process as a possible explanation for the formation of fossil flux transfer events in the magnetosphere and the formation of the low‐latitude boundary layer.