Evaluation of ionospheric models for Central and South Americas

Telmo Dos Santos Klipp,Adriano Petry,Jonas Rodrigues De Souza,Gabriel Sandim Falcão,Haroldo Fraga De Campos Velho,Eurico Rodrigues De Paula,Felix Antreich,Mainul Hoque,Martin Kriegel,Jens Berdermann,Norbert Jakowski,Isabel Fernandez-Gomez,Claudia Borries,Hiroatsu Sato,Volker Wilken

doi:10.1016/j.asr.2019.09.005

Abstract

This work shows a 20-month statistical evaluation of different Total Electron Content (TEC) estimators for the Central and South America regions. The TEC provided by the International GNSS Service (IGS) in the area covered around the monitoring GNSS stations are used as reference values, and they are compared to TEC estimates from the physics-based (Sheffield University Plasmasphere Ionosphere Model—PIM) and the empirical (Neustrelitz TEC Model-Global—NTCM-GL) models. The mean TEC values show strong dependence on both solar activity and seasonal variation. A clear response was noticed for a period close to 27 days due to the mean solar rotation, as seen in the solar flux measurements. Consistently, the mean TEC values present an annual variation with maxima during December solstices for southern stations with geographic latitudes greater than 25° S. Semi-annual dependence has been observed in TEC for the sector between ±25° of geographical latitude but with modulations caused by fluctuation in the solar radiation. We observed a high correlation between solar radio flux F10.7 and NTCM-GL outputs. The fast increases in F10.7 index have caused significant differences between IGS data and NTCM-GL results mainly for equatorial and low latitudes. For the initial months of the evaluated period (January–April, 2016), the errors of the physics-based model were considerably larger, mainly near the equatorial ionization anomaly. The discrepancies observed in SUPIM results are mainly due to inputs of solar EUV flux. The EUVAC model has underestimated EUV flux between January and April, 2016, when the solar activity was moderated and Solar2000 model has overestimated such flux during low solar cycle period between May and August, 2017. In relation to IGS data, the two assessed models presented smaller differences during the June solstice season of 2016.

Highlights

Ionospheric modeling that provides accurate ionospheric delay has a direct impact on the Global Navigation Satellite Systems (GNSS) positioning accuracy (Subirana et al, 2013) enabling several applications for users of a single frequency, as for example, that ones of Satellite-Based Augmentation System (Rovira-Garcia et al, 2016)
The main purpose of this work is to validate the Total Electron Content (TEC) estimates of two models for equatorial and low latitude covering Central and South Americas using TEC provided by the International GNSS Service (IGS) which is supported by GNSS ground stations data
The two blue dots near the analyzed period extremities are examples of TEC values obtained with SUPIM considering the solar EUV flux given by Solar2000 and EUV flux model for aeronomic calculations (EUVAC) models

Summary

Introduction

Ionospheric modeling that provides accurate ionospheric delay has a direct impact on the Global Navigation Satellite Systems (GNSS) positioning accuracy (Subirana et al, 2013) enabling several applications for users of a single frequency, as for example, that ones of Satellite-Based Augmentation System (Rovira-Garcia et al, 2016). It can lead to a better understanding of ionospheric conditions but requires intensive data processing and a large amount of observational data in order to validate the results, mainly related to solar activity dependence, seasonal variations, and the global and regional morphology of the ionosphere. This work presents a 20-month statistical analysis using different ionospheric Total Electron Content (TEC) estimates for the Central-South American region, ranging from À90 W to À25 W longitude and from À65 S to 20 N latitude. The main purpose of this work is to validate the TEC estimates of two models for equatorial and low latitude covering Central and South Americas using TEC provided by the International GNSS Service (IGS) which is supported by GNSS ground stations data. The spatial and seasonal variations of the TEC as well as the dependencies caused by solar activity between January 2016 and August 2017 are analyzed

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Conclusion