Storms and the seasonal anomaly in the topside ionosphere

Abstract

Data from the Alouette-I topside sounder have been used to study the height and latitudinal electron distributions during the seasonal anomaly and during ionosphere storms. It is shown that in the daytime topside ionosphere, disturbance effects having similar features to those of the seasonal anomaly occur mainly during the main phase of magnetic storms and sometimes during active periods of the recovery phase. The importance of these characteristics in understanding the nature of the two phenomena is discussed. An attempt is made to explain quantitatively the seasonal anomaly as caused by changes in atmospheric composition near the turbopause ( n(O) decrease and n(N 2) and n(O 2) increase from winter to summer). The disturbance effects in the daytime F2-region and in the topside ionosphere during the main phase of magnetic storms are also interpreted in terms of changes in atmospheric composition near turbopause levels.