Ionospheric disturbance and electron precipitation from the outer radiation belt

Values of precipitated electron flux near the magnetic shell L = 4, observed by the satellite Alouette, are compared with ionospheric behavior at six stations that also lie near this shell. It is shown that there exists a critical value of the flux, the same for all stations, above which an ionospheric disturbance invariably occurs. These disturbances involve increased absorption in the D and lower E regions, with usually a decrease of ƒoF2 and an increase of h′F2. It is further shown that the percentage of time for which the critical flux is exceeded at each station is almost exactly the same as the percentage of time for which the ionosphere is disturbed. The conclusion is drawn that all such disturbances can be accounted for by electron precipitation.