Interaction of Magnetic Flux Ropes Via Magnetic Reconnection Observed at the Magnetopause

Using the high-resolution field and plasma data obtained from the Magnetospheric Multiscale mission at the magnetopause, a series of three flux transfer events was observed one after another inside southward ion flows, without time gap between any two successive flux ropes. Using the plasma measurements, the current densities within the flux ropes were studied in detail. The currents within the first two flux ropes, dubbed Fr1 and Fr2, were composed of a series of well-separated filamentary currents. The thickness of the filamentary currents and the gap between them were sub ion scale, occasionally dropped down to electron scale. In the third flux rope Fr3 which was closest to the expected reconnection X line, the current displayed a singular compact current layer, was ion scale in width and concentrated on its center. Considering the location of the flux ropes relative to the reconnection X line, we suggested that the current density could be a singular structure when the flux rope was just created and then fragmented into a series of filamentary currents as time. By examining the interregions between Fr1 and Fr2, and between Fr2 and Fr3, reconnection was only confirmed to occur between Fr2 and Fr3 and no reconnection signature was found between Fr1 and Fr2. It seems that magnetic field compression resulted from collision of two neighboring flux ropes is one necessary condition for the occurrence of the coalescence.