Topside observation of electron density variations (G-condition) at times of low magnetic activity
The so-called G-condition of the ionosphere (foF2 < foF1, with normal foF1) is investigated from the topside with the Alouette II satellite. In the absence of a severe magnetic disturbance, the condition is occasionally observed over a path length of the order of a thousand kilometers. In this case, one observes a characteristic development: in the F2 region at the levels below about 1000 km there is a systematic decrease of electron density to about one-half the original value, followed by a gradual increase to normal, and at the levels above about 1000 km there is a corresponding increase, followed by a decrease back to normal. This variation in electron density is accompanied, at levels below 2000 km, by significant increases in scale height. Cylindrical electrostatic probes carried on the satellite show, at the same time, increases in electron temperature. Possible interpretations of the observational data are discussed.