Vertical structures of the TEC enhancement at mid-latitudes in the morning and the daytime sectors

Local time dependence of Total Electron Content (TEC) enhancement at mid-latitudes was studied with GPS data of a low earth orbit (LEO) satellite and ground-based receivers. Enhancement of TEC was observed at mid-latitudes by low earth orbit satellites. It tends to appear during geomagnetic storm periods. The amplitude of this TEC enhancement was about 10 TECU. Its latitudinal width was from 5 degrees to 20 degrees and it appeared from 30 degrees to 70 degrees of the magnetic latitude. The local time dependence of this TEC enhancement at mid-latitudes was studied. Several low earth orbit satellites carried a GPS receiver to position the location of the satellites. TEC data between GPS satellites and low earth orbit satellites can be derived from the dual-frequency GPS data. This TEC data is the integration value of the electron density in the plasmasphere and the topside of the ionosphere. The peak and the bottom side of the ionosphere do not contribute to the LEO-TEC data. In this study, the TEC data of the GRACE satellite was used. The orbital altitude of GRACE is about 450km. The local time dependence of the TEC enhancement was studied statistically from 2003 to 2004. It was found that there were two maxima of TEC enhancement from 3LT to 5LT and from 14LT to 17LT. The enhancement of TEC at 15LT was observed at 60 degree of geomagnetic latitude on May 29, 2003. The amplitude of GRACE-TEC enhancement was about 10TECU, while the amplitude of TEC enhancement observed by the ground-based GPS receivers was about 15 TECU. This result indicates that two of third of TEC enhancement observed by the ground-based GPS receivers occurred above the topside ionosphere. The enhancement of TEC at 3LT was observed at 50 degree of geomagnetic latitude on May 20, 2003. The amplitude of GRACE-TEC enhancement was about 10 TECU. On the other hand, the amplitude of the ground-based TEC enhancement was smaller than 3 TECU. It was found that the vertical structure of TEC enhancement was different in the morning and the daytime. This result indicates that the generation process of TEC enhancement at mid-latitudes is different in the morning and the daytime.