Characteristics Of The Ionospheric Total Electron Content Based On The Measurements Of Global Navigation Satellites

There have been revolutionary changes for the sounding and researching theionosphere due to the widly use of the global navigation satellites. In this paper, weintroduced the methods to derive the ionospheric parameters, such as ionospheric TotalElectron Content (TEC), based on the refringence effect of the GPS singles. Based onthe long-time data set of GPS-TEC and radio occutation, we investigated the variationsof the ionospheric TEC over China region, the short-term forecasting of the ionosphericTEC, the universal time (UT) variation of the ionospheric TEC in the polar regions andthe characters of the E-layer dominated ionosphere in the polar region during the polarnight. Besides these, we also analyzed the ionospheric response to a geomagnetic stormduring its main phase in the polar region.We introduced a method to derive the vertical TEC from the slant TEC over the GPSsite on the ground firstly. Then, using the TEC data of33GPS sites from China CrustalMovement Observation Network and the NmF2data of10ionosonde sites in the year of2004, we did some systemativecomparative analysis between the variations of theionospheric TEC and NmF2over China. Generally speaking, there were almost thesame variations of the ionopsheric TEC and NmF2. However, the peak time of diurnalvariation of ionospheric TEC was earlier than NmF2; The day-to-day variation ofionospheric TEC was smaller than NmF2; The location of the northern crest of theequatorial anomaly identified from ionospheric TEC was at lower latitude than thatidentified from ionospheric NmF2, which is caused by the tilt of the top side ionospherebecause of the fountain effect.A short-term forecasting method for the ionospheric TEC in China region wasproposed as a member of the group. This method consists of two parts: the single stationforecasting and the regional ionospheric reconstruction. They adopt auto-correlationmethod and corrected Kriging method, respectively. Using the ionospheric TEC dataabove, we analyzed the prediction errors and the relative errors for this method in Chinaregion. The relative error is12%with1hour in advance. Based on the results oftheprediction errors, we provided possible ways for improving the accuracy of theprediction. The softwares of this method were also done and used in Chinameteorological administration.A new ionospheric parameter in the polar regions, mean Polar Electron Content(mPEC), was proposed. The variations of mPEC with UT were investigated in the polar regions.It can be found that the UT variation of the ionosphere was stronger in theAntarctic than that in the Arctic. The relative contribution of the photoionization andboth of the transport and paricles precipitation to the ionospheric electrons was alsoestimated. The photoionization is the main source of mPEC standing for the polarionosphere, which was60-70%in the Antarctic, while about75%in winter and87%inthe other seasons in the Arctic. The transport and paricles precipitation was moreimportant to mPEC in the Antarctic than that in the Arctic, which was50%of thephotoionization in the Antarctic, while only33%in winter and less than15%in theother seasons in the Arctic.The reason of thes characters were mainly caused by thetheseparation of the geomagnetic pole from the geographyic pole.The characters of the E-layer Dominated Ionosphere (ELDI) in the Antarctic duringpolar night was investigated and compared with that in the Arctic, firstly. The ELDI wasobvious in the polar region during polar night and its distribution was very similar withthe auroral oval. The occurrence of ELDI was higher in the night side, which was about70%in the Arctic and90%in the Antarctic. The ELDI was mainly caused by the highenergy particles precipitation. The difference of the distribution and the occurrence ofELDI between Antarctic and Arctic was because that the electron density was larger inthe Antarctic than Arctic, whose reason may associate with the difference of the neutralatmosphere and the separation of the the geomagnetic pole from the geographyic polebetween theAntarctic and Arctic.Based on the multi-observations, including GPS-TEC and radio occutation, theionospheric response to a typical geomagnetic storm was analysed in the Arctic regionduring its main phase. It was found that the increase of electron density in the E-layerwas very important for the positive geomagnetic storm, which was the supplement ofthe knowledge of ionosphere responding to this geomagnetic storm in the global region.