Studies On The Annual And Semiannual Anomalies And Storm Characteristics Of Mid- And Low Latitudes Ionosphere

Ionospheric climatology and ionospheric weather are two of the most important topics in the ionospheric field. The main task of the ionospheric climatology study is focused on the ionospheric annual and semiannual variations including winter anomaly (seasonal anomaly), semiannual anomaly (equinox anomaly) and December anomaly (non-seasonal anomaly or annual anomaly); the key of ionospheric weather is ionospheric storm. This thesis discussed most of its part on the ionospheric anomaly of annual cycle and storm behavior in the mid- and low latitudes.In the first half part of the thesis, we investigated the main features of the ionospheric annual and semiannual variations in the mid-and low latitudes. Early investigations of the F2-layer critical frequency revealed that it does not behave at all in the manner of a simple Chapman layer but displays many outstanding abnormal phenomena which may involve some basic mechanisms. To find out how these anomalies are produced may help us understand the fundamental physical and chemical processes that control the ionosphere behavior, and more importantly, is essential for the investigation of ionospheric storm. Based on the 13-year Topex satellite TEC data and CODE's 11-year GIMs (Global Ionospheric Maps), and with the method of Empirical Orthogonal Function (EOF) analysis as well as Fourier expansion, we had obtained the temporal anomaly information varied with magnetic latitudes and local time. The results revealed that though TEC annual and semiannual variations behave in the same way as shown in the F2-layer peak electron density, NmF2, their magnitudes are rather different. Based on 9-year topside ionospheric ion density data measured from DMSP satellites, we further study the topside ionospheric annual and semiannual variations. Results showed there is large annual anomaly and small semiannual anomaly in the topside ionosphere which testified the altitude dependence of the ionospheric annual and semiannual variations. It is suggested that different physical and chemical processes in the bottomside and topside ionosphere should responsible for this disparity. We also found that the amplitudes of seasonal anomaly, annual anomaly and semiannual anomaly are modulated by the solar activity, and found this modulation is different for topside ionosphere ion density and TEC which manifests an altitude dependence of solar modulation. Seasonal...