Comparison of GPS based TEC measurements with the IRI-2012 model for the period of low to moderate solar activity (2009–2012) at the crest of equatorial anomaly in Indian region

• Published in: Advances in space research 2015-04, Vol.55 (8), p.1965-1975
• Main Authors: Karia, S.P., Patel, N.C., Pathak, K.N.
• Format: Article
• Language: English
• Subjects: Anomalies; Electron density; Equatorial regions; Estimates; Global Positioning System; India; International reference ionosphere (IRI) model; Low latitude ionosphere; Mathematical models; Solar activity; Total electron content
• ISSN: 0273-1177; 1879-1948
• DOI: 10.1016/j.asr.2014.10.026

The measurements of total electron content (TEC) are conducted at Surat (21° 9′ N, 72° 47′ E) in India, which lies under the northern crest of the equatorial anomaly region, for a period of four years from low to moderate solar activity (2009–2012) using a Global Positioning System (GPS) receiver. These results are compared with the TEC derived from IRI-2012 using three different options of topside electron density: NeQuick, IRI01-corr and IRI-2001. As there is difference between the upper limit of integration in the GPS TEC (20,200km) and the IRI model (2000km), to have a fair comparison of measured TEC with that of modeled TEC, the plasmaspheric contribution to the GPS TEC is removed. The measured TEC are compared with the model derived TEC for different times of the day for all months of four years (2009–2012). The IRI-2012 estimates the TEC well for the dusk hours 1800LT and noon hour 1200LT from 2010 to 2012. However, the estimation shows discrepancies with the observed TEC in the year 2009. For 0600LT it is observed that, from 2009 to 2011 the predictions made by IRI-2012 (options NeQuick and IRI01-corr) shifts from over estimation (0–50%) to under estimation (50–75%) and estimate the TEC well in the year 2012. In general, from 2009 to 2012, it is observed that with ascending phase of solar cycle the discrepancies in IRI prediction decreases for 0600LT, 1200LT and 1800LT hours of the day. Further, the comparison is also done for TEC at peak hour 1430LT for four months i.e. April, June, October and December (representing four seasons). It is observed that the peak hour TEC obtained by model overestimates the TEC for a low solar activity year 2009 but estimates well in 2010 and 2012 (except June). Further, model underestimates the peak hour TEC for moderate solar activity year 2011.