Linear time-series modeling of the GNSS based TEC variations over Southwest Japan during 2011-2018 and comparison against ARMA and GIM models

A significant amount of research has been conducted in Southwest (SW) Japan on climate modeling, disaster management, earthquake prediction, precise positioning, datum definition, and reference frames. However, there is substantial scope for numerical modeling and forecasting of ionospheric Total Electron Content (TEC) variations over the region, which would be beneficial for further communication and navigation purposes. Therefore, in this study we examined spatio-temporal ionospheric TEC variations using long-term Global Navigation Satellite System (GNSS) measurements from 01 January, 2011 to 31 December, 2018 through a modified Linear Time-series Model (LTM) and substantiated our findings by comparing them with those of the existing empirical Global Ionospheric Map (GIM) and Auto-Regressive Moving Average (ARMA) methods. We analyzed TEC variations at 10 permanent stations covering three districts of SW Japan, which mainly include the Kyushu district and parts of the Chugoku and Shikoku districts. To determine the performance of the LTM, the geomagnetic (Northern Polar Cap (PCN) and Disturbance (Dst)) indices were included, together with the additional solar and planetary geomagnetic disturbance indices (F10.7 and Ap). Our comparison results show that the Root Mean Square Error (RMSE) values in terms of TEC units (TECUs) between the observed and the TEC predicted by the LTM vary from 1.57 to 1.66, which are better than those between the observed and the TEC predicted by the ARMA (1.84-1.93) and the GIM (9.67-9.84) TEC models. An analysis of the results emphasizes the superior performance of the LTM over the other models in terms of its discriminability of temporal, as well as spatial, components.