ISEE‐1 and 2 observations of magnetic flux ropes in the magnetotail: FTE's in the plasma sheet?

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Abstract
Magnetic field observations on ISEE‐1 and 2 in and near the neutral sheet about 20 Re down the near‐Earth magnetotail reveal the occurrence of structures resembling magnetic flux ropes. Both electric field and fast plasma data show that these structures convect across the spacecraft at speeds of 200 ‐ 600 km/s, and that they have scale sizes of roughly 3 ‐ 5 Re. The rope axis orientation is across the tail, approximately in the −Y GSM direction. Their magnetic structure is strikingly similar to magnetic flux ropes observed in the Venus ionosphere, and to flux transfer events observed at the dayside magnetopause. The total field‐aligned current within these ropes may approach a million amps. These structures may arise because of patchy reconnection within the plasma sheet, or may be tearing islands formed when the plasma sheet magnetic field has a cross‐tail component. Plasma sheet flux ropes are not a common feature at ISEE orbital altitudes; this suggests that near‐Earth neutral line formation within ISEE apogee (22 Re) may be equally rare.