We present 9‐ and 7‐day periodic oscillations in the global mean Total Electron Content (TEC) from 1 January 2005 to 31 December 2006. Spectral analysis indicates that the pronounced periodicities of 9 and 7 days observed in TEC are associated with variations in solar wind high‐speed streams and geomagnetic activity. Neutral temperature and winds near 250 km, measured by a Fabry‐Perot Interferometer at Resolute Bay, also exhibit 9‐ and 7‐day periodicities. These pronounced periodicities support simultaneous observations of 9‐ and 7‐day periodicities in thermosphere neutral density (Lei et al., 2008a; Thayer et al., 2008). It is anticipated that the ionospheric response at 9 and 7 days represents some combination of effects due to chemical loss, neutral winds, and disturbance dynamo‐driven electric fields.

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In this paper, we calculate the ionospheric global electron content (GEC) from the GPS TEC data along the geographic longitude 120°E during the period of 1996-2004, and investigate the relationship between GEC and 10.7 cm solar radio flux F 10.7 and its seasonal dependence with partial correlation analysis. Our results show that GEC is closely correlated with solar activity index F 10.7 and is also related with annual and semiannual variations. An empirical GEC model driven by those factors is then to examine the influences of different solar activity proxies for the model input. The results suggest that GEC mainly depends on solar activity and the seasonal variations; the latter is also modulated by solar activity. Furthermore, the magnitude of semiannual variation is a little greater than that of annual variation. Our empirical GEC model is proved to be better than the model proposed by Afraimovich et al. ionospheric global electron content, ionospheric climatology, empirical modelThe ionosphere is an important part of the near-earth space, whose state is largely determined by the general level of solar radiation. The most important causes of the ionospheric climatological variation are solar 11-year circular variation and seasonal variation due to the earth revolution around the sun. Total electron content (TEC) is an important ionospheric parameter playing a significant role in ionospheric climatological analysis [1][2][3] since the 1960s. Many related reports [4][5][6][7] have come out especially after the appearance of Global Positioning System (GPS), which brings convenience for studying the large-scale even global TEC variation because of its advantages such as plentiful observatories, wide distribution and continuous all-weather observation. All those reports point out that besides temporal variation (e.g., daily, semi-annual and annual variations), TEC also has spatial variation such as equatorial anomaly and spatial variation due to the unbalanced distribution of the sea and the land. It is a meaningful subject to investigate the climatology of ionospheric global electron content from the GPS TEC data. Recently, Afraimovich et al. [8] introduced a new parameter global electron content (GEC) using global TEC map data from 1998 to 2005, which are products of several laboratories (JPL, UPC, CODE, ESA and EMR) based on global ionospheric mapping (GIM) technology. GIM is two-dimensional curving grid with a resolution of 5° along the longitude and 2.5° along the latitude. GEC can eliminate the local characteristics of TEC and clearly show the whole profile of global ionosphere, therefore, it is superior to TEC to analyze global ionosphere and dynamical process [8] . Afraimovich et al. [8] found that GEC is closely related to solar activity when smoothed with a 1-year time window, and they also obtained a simple linear regression model between GEC and 10.7 cm solar radio flux F 10.7 with the potential seasonal dependence ignored. One purpose of this paper is to study the climatology of GEC in more