Seasonal Variations of GNSS TEC values in the Equatorial Ionospheric Anomaly Trough at Chuuk (geographic: 7.5° N, 151.0° E; geomagnetic: 0.4° N) in the Federated States of Micronesia during the solar maximum in 2014

The equatorial ionosphere shows large temporal variations and spatial gradients in electron density, and these structures can affect applications of Global Navigation Satellite System (GNSS). It is presented that the variations of the trough of the equatorial ionospheric anomaly (EIA) using GNSS total electron content (TEC) measurements from Chuuk (geographic: 7.5° N, 151.9° E; geomagnetic: 0.4° N) in Micronesia during the solar maximum in 2014. The daytime GNSS TEC values have a good correlation with solar rotation period, and it is significant in summer season. The semi-annual anomaly on the GPS TEC variation has the amplitudes of 12 TECU on March and 9 TECU on October, respectively, with a yearly aveage of 38 TECU. The equinoctial asymmetry at the March equinox was higher than that at the October equinox. Daily mean GPS TEC values were higher in December than in June, which could be interpreted as annual or winter anomalies. The pre-midnight GPS TEC increasing could be explained withe the slow loss process of electron that is largely produced duringthe daytime of equinox. Finally, we analyze the GPS rate of TEC index (ROTI) to study characteristics of the ionospheric irregularities in the EIA trough region, and then examine GPS positioning errors with GPS TEC and ROTI values.