GPS observations of TID events generated by the moving solar terminator

Abstract

GPS-TEC data from the International GNSS Services (IGS) were used in this paper to analyze the medium scale traveling ionospheric disturbances (MSTIDs) which are generated by the moving solar terminator (ST) during the quiet days in 2005. We collected the most comprehensive and dense GPS network's data from North-America region and introduce here a strategy that combines polynomial fitting and multi-channel maximum entropy spectral analysis to obtain TID parameters. The results of our study are summarized as follows: (1) MSTIDs stimulated by the moving ST (ST-MSTIDs) are detected at mid-latitudes after the passage of the solar terminator with the life time of 2 similar to 3 h and the variation amplitude of 0.2 similar to 0.8 TECU. Spectral analysis indicated that the horizontal wavelength, average period, horizontal phase velocity of the MSTIDs are around 300 +/- 150 km,150 +/- 80 m/s, and 25 +/- 15 min, respectively. In addition, ST-MSTIDs have wavefronts elongated in the moving ST direction and almost parallel to ST. (2) The statistical results demonstrate that the dusk MSTIDs stimulated by ST is more obvious than the dawn MSTIDs in summer days. On the contrary, the more-pronounced dawn MSTIDs occur in winter days. Further analysis indicates that the seasonal variations of ST-MSTIDs occurrence frequency are most probably related to the seasonal differences of the variations of EUV flux in the ionosphere region and recombination process during sunrise and sunset period at mid-latitudes.