An Empirical Orthogonal Function (EOF) Analysis of Ionospheric Electron Density Profiles Based on the Observation of Incoherent Scatter Radar at Millstone Hill

Abstract The empirical orthogonal function (EOF) analysis has been applied to studying the ionospheric electron density profiles between 160 and 700 km by using the data of the incoherent scatter radar at Millstone Hill from February 1976 to April 2006. The mean electron density profile and the first three terms of EOF series superposed on the mean term are fitted by Chapman‐α function respectively. The results reveal that the first three terms of EOF series control the main parameters of the electron density profiles: the first term mainly controls the ionospheric F2 peak density NmF2, the second controls both the F2 peak height hmF2 and the effective scale height Hm, and the third controls the effective scale height Hm. In addition, we have analyzed the diurnal, seasonal and solar activity variations of the corresponding coefficients of the EOF terms. These variations represent the climatic characteristics of NmF2, hmF2 and Hm, such as the ionospheric winter anomaly and semiannual anomaly. EOF series converge rapidly in analyzing the electron density profiles, and the first few terms can represent the main characteristics. So we can use EOF analysis to extract the main distributional characteristics as well as the diurnal and climatic variation characteristics of the electron density profiles, which can be used to build the empirical model for further study.