Global total electron content prediction performance assessment of the IRI-2016 model based on empirical orthogonal function decomposition

摘要

In this study, the empirical orthogonal function (EOF)decomposition technique was utilized to analyze the similarities anddifferences of the spatiotemporal characteristics between the total electroncontent (TEC) of the International GNSS Service global ionospheric map (GIM)and that derived from the International Reference Ionosphere 2016 (IRI-2016)model in 2013. Results showed that the main spatial patterns andtime-varying features of the data set have good consistency. The followingfour main spatiotemporal variation features can be extracted from both datasets through EOF decomposition: the variation with the geomagnetic latitudereflecting the daily averaged solar forcing, the diurnal and semidiurnalperiodic changes with longitude due to local time, and the interhemisphericasymmetry caused by the annual variation of the inclination angle of theEarth's orbit. The differences between the spatial patterns represented bythe EOF base functions of IRI-2016 and GIM TECs were analyzed by extractingthe same time-varying coefficients. The deviations of the interhemisphericasymmetry component between the two data sets showed roughly equal valuesthroughout the Southern or Northern Hemisphere, whereas those of the otherspatial modes were mainly concentrated on the equatorial region. Thedifferences of the time-varying characteristics between the IRI-2016 and GIMTECs were also compared by extracting the same EOF base functions. Althoughthe EOF coefficients of the two data sets presented consistent seasonalvariations, the magnitude of IRI-2016 TEC changes over time was less thanthat of GIM TEC. The diurnal variation of the daily averaged solar forcingcomponent and the annual variation of the interhemispheric asymmetrycomponent exhibited relatively large deviations between the two data sets.Considering the variance contribution of the different EOF components andtheir average relative deviations, both analyses showed that the dailyaveraged solar forcing and interhemispheric asymmetry components were themain factors for the deviation between the IRI-2016 and GIM TECs.