Solitary electromagnetic pulses detected with super-alfvénic flows in earth's geomagnetic tail

Solitary nonlinear (δB/B) electromagnetic pulses have been detected in Earth's geomagnetic tail accompanying plasmas flowing at super- Alfvénic speeds. The pulses in the current sheet had durations of 5 were left-hand circularly polarized, and had phase speeds of approximately the Alfvén speed in the plasma frame. These pulses were associated with a field-aligned current The wave activity was enhanced from below the ion cyclotron frequency to electron cyclotron and upper hybrid frequencies. The detailed properties suggest the pulses are nonlinearly steepened ion cyclotron or Alfvén waves.