Forecasting ionospheric VTEC in the Indian equatorial and low-latitude region amid geomagnetic storms using the VECM model

Abstract

Geomagnetic storms are one of the major causes of irregular variations in the ionosphere. The effect of a geomagnetic storm on Vertical Total Electron Content (VTEC) variation, especially in the equatorial regions, is very complex and uncertain due to the Equatorial Ionization Anomaly (EIA). Thus, the VTEC exhibits large and complex spatio-temporal variations in the equatorial region. A deeper study of the relationship between the past values of geomagnetic storm variables and the present value of VTEC, and vice versa can help better understand the dynamics of the variables and processes’ long-term equilibrium between the variables. Causal dependence between the variables has been found helpful in determining the temporal dependencies in econometrics where parameters are uncertain, and variability patterns are complex. In this study, causality was used for investigating the impact of the highly complex geomagnetic processes on VTEC. Causality between the geomagnetic indices and deviation in VTEC was investigated to understand the interconnection between the dynamical variables, the nonlinear correlations between them, and the underlying physical processes to predict the deviation in VTEC. Based on causality, a Vector Error-Correction (VECM) forecast model was developed for a two-step ahead forecast of VTEC on geomagnetic storm days. The forecast results were compared with the actual values of GPS VTEC and the International Reference Ionosphere (IRI) model. Two metrics, namely RMSE and the correlation coefficient, were used to test the performance. The forecasted values were compared with the actual values, and the RMSE and correlation coefficients were calculated. The model’s performance was also compared with the reference model IRI 2016. For most of the days, the model could predict with low RMSE for two-step-ahead prediction (1 h). Keywords: Ionosphere; Geomagnetic storm; Causality; TEC