Monitoring the global-scale winter anomaly of total electron contents using GPS data

The winter anomaly phenomenon of Total Electron Contents (TEC) at latitudes 15°-60°N and 15°S-60°S is presented using GPS carrier-phase data obtained from GPS stations during 2002. The correlation between the [O/N2] ratio estimated using the NRLMSISE-00 atmospheric model and the TEC winter anomaly is also investigated. The numerical results show that the TEC winter anomaly in different regions of the world tends to be dominated by different factors. In North America, the TEC winter anomaly is strongly affected by the magnetospheric processes in high latitudes and the [O/N2] ratio. In the Euro-Africa and Russia-Asia regions, the TEC winter anomaly depends mainly on the [O/N2] ratio at the latitude band of 30°-60°N, and the extent of the TEC winter anomaly gradually decreases from 60°N to 30°N. The extent of the TEC winter anomaly increases at the latitude band of 15°-30°N due to the influence of the meridional neutral wind and the seasonal changes of the subsolar point. However, the TEC winter anomaly was not observed in southern hemisphere in 2002. The TEC equinoctial asymmetries in the northern and southern hemisphere are also presented using GPS TEC values collected in March and September 2002.