Feasibility study on the derivation of the O+‐O collision frequency from ionospheric field‐aligned observations

Recently, Vickers et al. (2013) used a simplified ion momentum equation to derive the ion‐neutral (O+‐O) collision frequency and thermospheric atomic oxygen density from the European Incoherent Scatter Svalbard Radar data. It was assumed that the vertical neutral wind at high latitudes is generally small under geomagnetically quiet conditions so that it was neglected in their derivation. Although the vertical neutral wind may indeed be small, the field‐aligned neutral wind component, which needs to be taken into consideration in the ion momentum equation, can be large. Simulations with the Thermosphere‐Ionosphere Electrodynamics Global Circulation Model have been carried out to evaluate the effect of the neutral wind on the estimation of the ion‐neutral collision frequency from the ion momentum equation. Our results reveal that, even at high latitudes, the effect of the neutral wind can be significant in the derivation of the ion‐neutral collision frequency from ionospheric field‐aligned observations, especially at night.

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