A theoretical study of the high‐latitude winter F region at solar minimum for low magnetic activity

We combined a simple plasma convection model with an ionospheric‐atmospheric composition model in order to study the high‐latitude winter F region at solar minimum for low magnetic activity. Our numerical study produced time dependent, three‐dimensional ion density distributions for the ions NO + , O 2 + , N 2 + , 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 one complete day. The main result we obtained was that high‐latitude ionospheric features, such as the ‘main trough,’ the ‘ionization hole,’ the ‘tongue of ionization,’ the ‘aurorally produced ionization peaks,’ and the ‘universal time effects,’ are a natural consequence of the competition between the various chemical and transport processes known to be operating in the high‐latitude ionosphere. In addition, we found that (1) the F region peak electron density at a given location and local time can vary by more than an order of magnitude, owing to the UT effect that results from the displacement between the geomagnetic and geographic poles; (2) a wide range of ion compositions can occur in the polar F region at different locations and times; (3) the minimum value for the electron density in the main trough is sensitive to nocturnal maintenance processes; (4) the depth and longitudinal extent of the main trough exhibit a significant UT dependence; (5) the way the auroral oval is positioned relative to the plasma convection pattern has an appreciable effect on the magnetic local time extent of the main trough; (6) the spatial extent, depth, and location of the polar ionization hole are UT dependent; (7) the level of ion production in the morning sector of the auroral oval has an appreciable effect on the location and spatial extent of the polar ionization hole; and (8) in the polar hole the F region peak electron density is below 300 km, and at 300 km, diffusion is a very important process for both O + and NO + . Contrary to the suggestion based on an analysis of AE‐C satellite data obtained in the polar hole that the concentration of NO + ions is chemically controlled, we find diffusion to be the dominant process at 300 km.