Statistical analysis of travelling ionospheric disturbances using TEC observations from geostationary satellites

Certain modern radio systems that rely on trans-ionospheric propagation require knowledge of the changes in the ionosphere that can be characterised by changes in total electron content (TEC). An important cause of these TEC fluctuations is travelling ionosphere disturbances (TIDs). Temporal variations of European mid-latitude TEC measurements obtained from geostationary satellites across two solar cycle phases, i.e. solar minimum from 1975 to 1976 and solar maximum from 1989 to 1990, were studied. The frequencies and amplitudes of the TIDs were investigated using direct time series analysis, discrete wavelet analysis and Fourier analysis. Results show that the solar maximum TIDs are larger in absolute amplitude but comparable in percentage amplitude (relative to daily TEC maximum) in relation to the solar minimum TIDs. The largest daily amplitudes of the TIDs were distributed between 2.5% and 17% across the data set without a clear dependency on solar cycle phase. TIDs were found at all of the periods studied between roughly 20 min and 3 h, with the most common periods around 1.7-2 h. Throughout the solar cycle the TIDs had the largest amplitudes during winter, with a secondary peak in TID activity in summer at solar maximum.