Theoretical predictions for ion composition in the high‐latitude winter F‐region for solar minimum and low magnetic activity

Abstract

We combined a simple plasma convection model with an ionospheric‐atmospheric density model in order to study the ion composition in the high‐latitude winter F‐region at solar minimum for low geomagnetic activity. Our numerical study produced time‐dependent, 3‐dimensional, ion density distributions for the ions NO+, O2+, N2+, O+, N+, and He+. We covered the high‐latitude ionosphere above 54°N magnetic latitude and at altitudes between 160 and 800 km for a time period of 1 complete day. From our study we found the following (1) The ion composition exhibits a significant variation with latitude, local time, altitude, and universal time. (2) The variations of the ion composition with latitude and local time are in good agreement with the Atmosphere Explorer measurements both quantitatively and qualitatively. (3) At times and at certain locations the molecular ion density can be comparable to the O+ density at 300 km, and at 200 km the O+ density can be comparable to the molecular ion density. These results have important implications for the interpretation of incoherent scatter radar spectra obtained at high‐latitudes. (4) Different ground‐based observation sites should measure different diurnal variations in ion composition even if these sites are approximately at the same magnetic latitude owing to the UT response of the high‐latitude ionosphere. (5) A satellite in a 300 km circular polar orbit should measure large orbit to orbit variations in both electron density and ion composition, again owing to the UT response of the polar ionosphere. (6) Erroneous conclusions can be drawn about ion density scale heights if the variations along the track of a satellite in a highly elliptical polar orbit are assumed to be only due to altitude variations.