The middle-latitude F region during some severe ionospheric storms

Topside ionograms taken during some severe ionospheric storms show F2-layer critical frequencies that are less than F1-layer critical frequencies. A comparison of the electron density profiles derived from Alouette I ionograms obtained during these disturbed periods with those obtained during undisturbed periods show that the height of the F2 layer moves up, the plasma scale height above the F2 peak increases, and the column electron content up to 1000 km decreases. Data taken during the April 18, 1965, storm are treated in detail and it is found that an increase in the electron loss rate by a factor of 16 times the undisturbed rate can account for the decrease in electron density.