Self-consistent modelling of the daytime electron density profile in the ionospheric F region

Abstract. A theoretical self-consistent method for the description of daytime N_e(h) profiles in the ionospheric F region measured by EISCAT is proposed. It is based on the use of a theoretical F-region model and measured electron density, N_e(h), electron, T_e(h), and ion temperature, T_i(h), and field-aligned plasma drift V_l(h) profiles. The method describes the observed N_e(h) profile with high accuracy for quiet and disturbed conditions. Two versions of the method are considered: in the first the exospheric temperature T_ex is derived from a procedure minimizing [log(N_e(h)_obs / N_e(h)_cal]², in the second T_ex is deduced from the ion energy conservation in the F region. The method allows us to infer from the incoherent-scatter observations: concentrations of atomic oxygen, [O], molecular oxygen, [O₂], molecular nitrogen, [N₂] the vertical plasma drift, W, the exospheric temperature. T_ex, and the shape parameter S in the neutral temperature profile. The ratio ([O⁺]/N_e) calculated by the theoretical model is used to correct T_e(h), T_i(h) and N_e(h) profiles routinely measured with EISCAT which are known to depend strongly on the actual applied ion-composition model. Such a correction is especially important for geomagnetically disturbed periods when the F region is strongly enriched with molecular ions. We conclude that four of the six thermospheric parameters, namely [O], [N₂], W and T_ex can be confidently inferred from the EISCAT observations, while the other two derived parameters, [O₂] ans S are less reliable. The method can be used for the analysis of long-term (seasonal, solar cycle) as well as for day-to-day variations of the thermospheric parameters and the F-region ion composition using daytime incoherent-scatter observations.