A global model: Empirical orthogonal function analysis of total electron content 1999-2009 data

A global ionospheric total electron content (TEC) model based on the empirical orthogonal function (EOF) analysis method is constructed using the global ionosphere maps provided by Jet Propulsion Laboratory during the years 1999–2009. The importance of different types of variation to the overall TEC variability as well as the influence of solar radiation and geomagnetic activity toward TEC can be well represented by the characteristics of EOF base functions Ek and associated coefficients Pk. The quick convergence of EOF decomposition makes it possible to use the first four orders of the EOF series to represent 99.04% of the overall variance of the original data set. E1 represents the essential feature of global spatial and diurnal variation of the TEC. E2 contains a hemispherically asymmetric pattern manifesting the summer‐to‐winter annual variation. E3 and E4 can well reflect the equatorial anomaly phenomenon. P1 contains an obvious solar cycle variation pattern as well as annual and semiannual variation components. P2 mainly includes an annual fluctuation component. P3 has a strong annual variation and a weak seasonal variation pattern. P4 has both evident annual and semiannual oscillation components. The Fourier series as a combination of trigonometric and linear functions are used to represent the solar cycle, annual, and semiannual variation of the coefficients. Therefore the global TEC model is established through incorporating the modeled EOF series. The accuracy and quality of the model have been validated through the model‐data comparison, which indicates that the model can reflect the majority of the variations and the feature of temporal‐spatial distribution of the global ionospheric TEC. Key Points Uses EOF method to build the TEC empirical model Presents a new coordinate system based on local time and magnetic dip latitude Shows global‐scale, regional, and single‐station inspection for model validation