Validity of Different Global Ionospheric TEC Maps over Indian Region

The global ionosphere total electron content (TEC) maps regularly archived by the international GNSS services (IGS) and its associate analysis centers (IAACs) serve as the important ionospheric products meant for single frequency receiver users, ionospheric analysis and model reliability validation. At present, there are eight IAACs producing global ionosphere maps (GIMs) following their own mathematical procedure which are then combined together to develop the IGS final GIMs. Several researchers in the past used the final or individual IAAC GIMs for validating their mathematical model formulations, regional/global ionosphere maps. However, it has been realized that the reliability of these maps differs with locations/regions depending on various facts like density of IGS GNSS stations, geomagnetic coordinates, seasons and solar activity. We tried to evaluate the performance of various GIMs at a near equatorial station in Bangalore, India (IISC; 13.02°N, 77.54°E) and a far equatorial station in Jomsom, Nepal (JMSM; 28.81°N, 85.74°E) low latitude stations by comparing with the observed TEC derived from global positioning system (GPS) receivers. The results show that EMRG GIMs are more reliable at Bangalore as opposed to the least performance of ESAG GIMs regardless of ionospheric conditions. Concerning Jomsom, the CASG and UPCG GIMs show fairly better performance among all the models whereas the least performance is realized in EMRG and CODG GIMs during the quiet and disturbed ionospheric conditions, respectively. The results give an insight to revisit the grid point accuracy of GIMs for positioning, further understanding of ionospheric variability, and a fair selection of GIMs as reference values while accessing regional ionosphere maps or model developments.