Solitary Electromagnetic Pulses Detected with Super-Alfvénic Flows in Earth’s Geomagnetic Tail

Abstract

Solitary nonlinear ( δB=B >> 1) electromagnetic pulses have been detected in Earth’s geomagnetic tail accompanying plasmas flowing at super-Alfvenic speeds. The pulses in the current sheet had durations of ∼5 s, were left-hand circularly polarized, and had phase speeds of approximately the Alfven speed in the plasma frame. These pulses were associated with a field-aligned current Jₗₗ and observed in low density (0:3 cm⁻³), high temperature (Te ∼ Ti ∼ 3 x 10⁷ K), and β ∼ 10 plasma that included electron and ion beams streaming along B. 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 Alfven waves.