Variations in total electron content and other ionospheric parameters associated with magnetic storms

The storm-time variations of the ionosphere in middle latitudes during ionospheric storms are described. Usually the total electron content is increased during the first 24 hours of the storm. The total content then falls to below its quiet-day value and recovers after one or two days. The peak electron concentration in the F region is similarly increased at the beginning of the storm and is later depressed. The fall in peak electron concentration commences some hours earlier than the fall in total electron content. The equivalent slab thickness is increased above the quiet-day value throughout the storm, corresponding to an increase in the electron-ion temperature. In weak magnetic storms the ionospheric disturbance may not last longer than one day, and only the initial elevation of total electron content occurs.