A STUDY OF THE CHANGES IN THE F-REGION DURING SEVERE MAGNETIC STORMS

A study is presented of the F-region changes associated with three severe magnetic storms during the IGY period. The h'-f data from Washington D.C., Panama, Talara and Huancayo Stations, which lie close to the 75 degree W meridian, are used and the corresponding N-h profiles are derived using Budden's method. The N-h profiles are studied in terms of: (1) Storm changes in the N sub m F and h(.9N sub m F), (2) The total electron content up to 200 km and between 200-300 km, and (3) The vertical drift velocities during storms. The storm changes in N sub m F and h(.9N sub m F) indicate that large height deviations of the order of 200 km may occur during severe storms. The vertical drift velocities during storms computed from the experimental N-h profile data reveal upward drifts. These drifts produced by the disturbance fields are found to be of the same order as the quiet day drifts. It is found that the total electron content up to 200 km is relatively unaffected by storms and that the electron content between 200-300 km is decreased, at least during the first day of the storm in lower latitudes, by about 20-50%. The time sequence of the ionospheric events during storms is believed due to the hydromagnetic effects of the interaction between solar plasma and geomagnetic field. (Author)