Anomalous structure of the mid-latitude ionospheric F region on June 5, 9, and 10, 1991

The structure and dynamics of the mid-latitude ionosphere over Millstone Hill at high solar activity under geomagnetically quiet conditions in the period from June 5 to June 10, 1991, have been studied using the model of ionosphere-plasmasphere coupling. The mechanisms of formation of the anomalous structure of the ionospheric F region during the geomagnetic storms of June 5, 9, and 10, 199 1, have been studied. It has been indicated that the variations in the electric field perpendicular to the geomagnetic field and the plasma drift velocities are not the main factors of the formation of ionospheric condition G under study. The correction of the molecular nitrogen and oxygen densities and of the temperature of the neutral atmosphere model (MSIS-86) makes it possible to coordinate the calculated and measured NmF2 values and the attitude profiles of electron density and temperature and to explain the existence of condition G observed in the ionospheric F region on June 5, 9, and 10, 1991. The increased (as compared to the geomagnetically quiet conditions) content of molecular nitrogen and oxygen is the main cause of formation of the anomalous structure of the ionospheric F region on June 5, 9, and 10, 1991.