Ion‐beam‐driven electrostatic hydrogen cyclotron waves on auroral field lines

It is shown analytically and by means of plasma numerical simulations that the large amplitude hydrogen cyclotron waves on auroral field lines near 1 RE altitude may be excited by upward flowing ion beams rather than by field‐aligned currents. The large amplitude electric field near ω ≈ 0 is identified as the ion gyro‐harmonic waves on the beam ions observed in the frame of background ions and, therefore, such a wave exists only when the instability is excited by ion beams. Both the theory and numerical simulations support the conclusion.