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

摘要

A theoretical self-consistent method for thedescription of daytime N_e(h) profiles in the ionospheric Fregion measured by EISCAT is proposed. It is based on the use of a theoreticalF-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 methoddescribes the observed N_e(h) profile with high accuracy forquiet and disturbed conditions. Two versions of the method are considered: inthe first the exospheric temperature T_ex is derivedfrom a procedure minimizing [log(N_e(h)_obs / N_e(h)_cal]2, in the second T_ex is deduced from the ion energyconservation in the F region. The method allows us to infer from theincoherent-scatter observations: concentrations of atomic oxygen, [O], molecularoxygen, [O₂], molecular nitrogen, [N₂]the vertical plasma drift, W, the exospheric temperature. T_ex, and the shape parameter S in the neutraltemperature profile. The ratio ([O+]/N_e) calculatedby the theoretical model is used to correct T_e(h), T_i(h) and N_e(h) profiles routinely measured with EISCAT which are knownto depend strongly on the actual applied ion-composition model. Such acorrection is especially important for geomagnetically disturbed periods whenthe F region is strongly enriched with molecular ions. We conclude that four ofthe six thermospheric parameters, namely [O], [N₂], W and T_ex can beconfidently inferred from the EISCAT observations, while the other two derivedparameters, [O₂] ans S are less reliable.The method can be used for the analysis of long-term (seasonal, solar cycle) aswell as for day-to-day variations of the thermospheric parameters and theF-region ion composition using daytime incoherent-scatter observations.