Disruption of the magnetotail current sheet observed by AMPTE/CCE

Abstract

The Active Magnetospheric Particle Tracer Explorers/Charge Composition Explorer (AMPTE/CCE), with a small inclination of 4.8° and an apogee of ∼8.8 R E , is capable of exploring the dynamical behavior of the near‐earth magnetotail current sheet during substorms. At ∼1153 UT on day 240 (August 28), 1986, the spacecraft was on the midplane of the magnetotail near midnight (∼23.4 h LT) at a radial distance of ∼8 R E , when the onset of a substorm took place. The magnetic field data for the ∼3.5‐min interval following the onset indicated a variation of the magnetic field that has not been observed by geostationary satellites or by other spacecraft flown in the near‐earth tail ( r ≲ 20 R E ). The variation was characterized by a large‐amplitude (from less than 10 nT to greater than 40 nT) oscillation of the total field with a period of ∼13 s and also by southward turning of the field during most cycles of the oscillation. At times the magnetic field became strongly southward, and in a few measurements the magnitude of the southward component exceeded 20 nT. The level of high‐frequency perturbations (periods shorter than ∼10 s) was also enchanced during the event. The observations may be due to the formation of an X‐type neutral line and its motion near the spacecraft.