Magnetospheric convection and the high‐latitude F 2 ionosphere

Behavior of the polar ionospheric F layer as it is convected through the cleft, over the polar cap, and through the nightside F layer trough zone is investigated. Passage through the cleft adds of the order of 2 × 10 5 ions cm −3 in the vicinity of the F 2 peak and redistributes the ionization above approximately 400‐km altitude to conform with an increased electron temperature. The redistribution of ionization above 400‐km altitude forms the ‘averaged’ plasma ring seen at 1000‐km altitude. The F layer is also raised of the order of 20 km in altitude by the convection electric field. The time required for passage across the polar cap (25°) is about the same as that required for the F layer peak concentration to decay by e . The F layer response to passage through the nightside soft electron precipitation zone should be similar to but less than its response to passage through the cleft. The exception is that the layer will be lowered in altitude by the convection electric field. After leaving the night soft electron precipitation zone the layer decays, primarily by chemical recombination, as it convects equatorward and around the dawn side of the earth. In the absence of ionization sources, decay by factors of the order of 10²–10³ could occur prior to entry into the sunlit hemisphere, and thus the F layer night trough is formed.