Global mapping of total electron content from GNSS observations for updating IRI-Plas model

Abstract

Global median empirical model of Total Electron Content (GTEC) is developed driven by re-calibrated sunspot numbers, SSN2, for the quiet geomagnetic conditions (ap < 15 nT). The model is based on Spherical Harmonic Analysis (SHA) of Global Ionospheric Maps GIM-TEC provided by JPL from 1996 to 2019. The SHA coefficients are calculated for low solar activity (SSN2 ≤ 20) and high solar activity (SSN2 ≥ 100) and linear interpolation is applied between them. The input parameters of the model are the geographic coordinates, time UT, day, month, year, and the sunspot number SSN2. The GTEC mapping accuracy is validated by comparing results of GTEC, IRI-2016 and IRI-Plas models with the independent median GIM-TEC observed by JPL and UPC for four seasons and local time of moderate solar activity (2012). The results testify that GTEC shows Root Mean Square Error, RMSE, about 2 times less than that of IRI-2016 and IRI-Plas TEC predictions. Model GTEC can be used alone for GIM-TEC prediction under quiet conditions. It is also incorporated as an option to IRI-Plas code to improve accuracy of TEC predictions with IRI-Plas model.