Desenvolvimento de modelagem espectral para reconstrução do mapa de TEC utilizando o índice F10.7

Abstract

In the ionosphere, the variations of Total Electron Content (TEC) are strongly related to the solar activity, which can be evaluated using F10.7 index. In this context, it was developed a method to reconstruct the TEC maps daily variation for any given F10.7 value. The method is based on the analysis of a three-years period (2014-2016) of TEC data provided by The International GNSS Service (IGS), and the correspondent daily F10.7 index values in the period, produced by the Solar Irradiance Platform (SIP). Each geographic location in IGS TEC maps was evaluated individually, and the set of TEC values for a given day is first transformed to the frequency domain by applying the Discreet Fourier Transform (DFT) and then associated to the correspondent F10.7 value. The process is repeated for every day in the period evaluated, and individual plots of each one of the DFT coefficients versus F10.7 values were generated. After that, a linear regression technique was used to estimate the best fit to the data, using the Least Squares Method. The resulting linear curves (one for every DFT coefficient, in every geographic location) were able to model the TEC variability for any F10.7 value by just reversing the process, i.e. the curves are used to estimate the correspondent DFT coefficients, and the inverse DFT of these coefficients provides TEC variability in a day. Comparisons for the year 2017, not used in the modelling process, between IGS data and the reconstructed TEC maps using the proposed approach showed good agreement with daily and seasonal TEC variations. We observed daily Root Mean Squared Error (RMSE) close to 5 TECU in the whole period, except in three occasions, with duration of 2-8 days each, possibly related to unusual fast F10.7 peak events due to geomagnetic perturbations. Geographic distribution of error showed slight increase near magnetic Equator.