Acceleration of hydrogen ions and conic formation along auroral field lines

Electrostatic ion cyclotron turbulence and the formation of ion conics at low altitudes (≈ 1500 km) along auroral field lines have been investigated analytically and by plasma numerical simulations. Ion cyclotron waves are assumed to be driven unstable by the upgoing cold ionospheric electrons associated with the downward auroral current. When the electron drift speed is comparable to the electron thermal speed, it was found that the large‐amplitude ( e ϕ/ T e ≈ 1) coherent (ω = Ω i ) ion cyclotron waves should exist along auroral field lines at low altitudes extending a few hundred kilometers. Ion conics are associated with ion cyclotron turbulence, and the ion bulk temperature is found to increase by a factor of 10 from the initial ionospheric temperature, while the temperature of the high‐energy tail can be as much as 100 times the ionospheric temperature. Theory and simulations are in good agreement.