Longitudinal and Seasonal Variability of Equatorial Ionospheric Irregularities and Electrodynamics

The impact of the St. Patrick's Day storm (17 March 2015) on the major equatorial electro-dynamical process viz., the Equatorial Ionization Anomaly (EIA) has been assessed using 2D (5 ° lat. x 5 ° long.) total electron content (TEC) maps generated from the ground based SBAS (Satellite Based Augmentation System) enabled receiver data. The various aspects of EIA specifically the i) evolution/devolution, ii) longitudinal structure, and iii) its variability during different phases of a geomagnetic storm, have been brought out. These 2D TEC maps, which have a large latitudinal (5 S-45° N) and longitudinal (55-110° E) coverage, show the complete reversal in the longitudinal structure/pattern of EIA during the recovery phase of the storm as compared to the quiet day. These results have been explained in the light of the combined effects of the storm associated processes such as i) the penetration electric fields of magnetosphere origin, ii) storm-induced thermospheric winds, and, iii) activation of the consequent disturbance dynamo effectively distorting the longitudinal wave number 4 (WN4) structure of the EIA. It has been shown unambiguously that even a separation of ~10°-15° longitude could experience significantly different forcings. The relevance and the far reaching consequences of the study in the light of the current trends and requirements for reliable satellite based navigation are highlighted.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2016SW001408

The impact of the 17 March 2015 St. Patrick's Day storm on the evolutionary pattern of equatorial ionization anomaly over the Indian longitudes using high‐resolution spatiotemporal TEC maps: New insights

Abstract The present paper investigates accuracy of single and dual-frequency Global Positioning System (GPS) standard point positioning solutions employing different ionosphere error mitigation techniques. The total electron content (TEC) in the ionosphere is the prominent delay error source in GPS positioning, and its elimination is essential for obtaining a relatively precise positioning solution. The estimated delay error from different ionosphere models and maps, such as Klobuchar model, global ionosphere models, and vertical TEC maps are compared with the locally derived ionosphere error following the ion density and frequency dependence with delay error. Finally, the positional accuracy of the single and dual-frequency GPS point positioning solutions are probed through different ionospheric mitigation methods including exploitation of models, maps, and ionosphere-free linear combinations and removal of higher order ionospheric effects. The results suggest the superiority of global ionosphere maps for single-frequency solution, whereas for the dual-frequency measurement the ionosphere-free linear combination with prior removal of higher-order ionosphere effects from global ionosphere maps and geomagnetic reference fields resulted in improved positioning quality among the chosen mitigation techniques. Conspicuously, the susceptibility of height component to different ionospheric mitigation methods are demonstrated in this study which may assist the users in selecting appropriate technique for precise GPS positioning measurements.

Evaluation of GPS Standard Point Positioning with Various Ionospheric Error Mitigation Techniques

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https://hal.archives-ouvertes.fr/hal-03162179/document

Geomagnetic Activity Control of Irregularities Occurrences Over the Crests of the African EIA

The ionosphere is the region of the upper atmosphere and the study of the upper atmosphere has a significant role in monitoring, modeling and forecasting for satellite based navigation services. As India lies in a low latitude region, a more careful approach has to be taken to characterize the ionosphere due to the irregularities and equatorial anomaly conditions. In order to study the ionospheric temporal variations, a regional ionospheric model based on the Adjusted Spherical Harmonic Analysis (ASHA) is implemented. The results indicate that the ASHA model is one of the contenders for estimating ionospheric delays well for GNSS augmentation systems.

Modelling of ionospheric time delays based on adjusted spherical harmonic analysis

Satellite-Based Augmentation Systems (SBASes) are designed to provide additional accuracy and robustness to existing satellite-based radio navigation systems for all phases of a flight. However, similar to navigation systems such as GPS which has proven its worth for the investigation of the ionosphere, the SBASes do have certain advantages. In the present paper, we propose and demonstrate SBAS applicability to ionospheric and space weather research in a novel and cost-effective way. The recent commissioning of the Indian SBAS, named GPS Aided Geo Augmented Navigation (GAGAN), covering the equatorial and low-latitude regions centered around the Indian longitudes provides the motivation for this approach. Two case studies involving different ionospheric behavior over low-latitude regions vindicate the potential of SBAS over extended areas.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2014SW001103

Satellite‐based augmentation systems: A novel and cost‐effective tool for ionospheric and space weather studies

The present paper characterizes the L-band scintillation over Indian region using the long term database from GAGAN (GPS Aided GEO Augmented Navigation) network. Around 20 scintillation monitoring receivers are operating continuously under the GAGAN network from the year 2004 onwards.

https://www.ursi.org/Proceedings/ProcGA14/papers/ursi_paper2790.pdf

C. R. Sudhir

Papers

Satellite‐based augmentation systems: A novel and cost‐effective tool for ionospheric and space weather studies

Statistically characterizing the L-band scintillation over Indian equatorial and low latitude region