High-altitude and high-latitude O⁺ and H⁺ outflows: the effect of finite electromagnetic turbulence wavelength

Abstract. The energization of ions, due to interaction with electromagnetic turbulence (i.e. wave-particle interactions), has an important influence on H⁺ and O⁺ ions outflows in the polar region. The effects of altitude and velocity dependent wave-particle interaction on H⁺ and O⁺ ions outflows in the auroral region were investigated by using Monte Carlo method. The Monte Carlo simulation included the effects of altitude and velocity dependent wave-particle interaction, gravity, polarization electrostatic field, and divergence of auroral geomagnetic field within the simulation tube (1.2–10 earth radii, R_E). As the ions are heated due to wave-particle interactions (i.e. ion interactions with electromagnetic turbulence) and move to higher altitudes, the ion gyroradius ρ_i may become comparable to the electromagnetic turbulence wavelength λ_⊥ and consequently (k_⊥ρi) becomes larger than unity. This turns the heating rate to be negligible and the motion of the ions is described by using Liouville theorem. The main conclusions are as follows: (1) the formation of H⁺ and O⁺ conics at lower altitudes and for all values of λ_⊥; (2) O⁺ toroids appear at 3.72 R_E, 2.76 R_E and 2 R_E, for λ_⊥=100, 10, and 1 km, respectively; however, H⁺ toroids appear at 6.6 R_E, 4.4 R_E and 3 R_E, for λ_⊥=100, 10, and 1 km, respectively; and H⁺ and O⁺ ion toroids did not appear for the case λ_⊥ goes to infinity, i.e. when the effect of velocity dependent wave-particle interaction was not included; (3) As λ_⊥ decreases, H⁺ and O⁺ ion drift velocity decreases, H⁺ and O⁺ ion density increases, H⁺ and O⁺ ion perpendicular temperature and H⁺ and O⁺ ion parallel temperature decrease; (4) Finally, including the effect of finite electromagnetic turbulence wavelength, i.e. the effect of velocity dependent diffusion coefficient and consequently, the velocity dependent wave-particle interactions produce realistic H⁺ and O⁺ ion temperatures and H⁺ and O⁺ toroids, and this is, qualitatively, consistent with the observations of H⁺ and O⁺ ions in the auroral region at high altitudes.