Empirical Orthogonal Functions of the Australian Regional Ionosphere

Understanding the natural background variability of the ionosphere is required for investigations of the ionospheric response to external perturbations. Decomposition of ionospheric observations into a set of spatiotemporal structures allows the separation of the anomalous response of the ionosphere from the background variability. This paper presents preliminary results of the analysis of Australian regional Total Electron Content (TEC) using an Empirical Orthogonal Function (EOF) technique to distinguish the variability of the ionosphere caused by the solar and geomagnetic activity. TEC data at evenly distributed grid points was estimated using the Spherical Cap Harmonic Analysis (SCHA) method, applied to GPS data collected from the Australian Regional GPS Network (ARGN). This approach yields more detailed maps of regional TEC variation than can be obtained using global models. EOF analysis was used to decompose the TEC data set into a series of orthogonal Eigenfunction (EOF base function) and associated coefficients. The base function represents the variation in TEC with latitude and longitude. The coefficients represent the variation with time. Analysis of a year worth of data from 2010 yielded the following results: The first 5 EOFs describe 95% of the total TEC variance. The equatorial zone dominates in the spatial structure of the first EOF. This mode has a distinct diurnal and seasonal evolution its proportion is ~65% and highly correlates with the solar activity. Keywords: EOF, Equatorial Anomaly, Regional, SCHA, TEC, GPS, Australia .