Studies of the ionospheric ionization over Athens using ground ionosonde and GPS derived TEC values

In the frame of this investigation systematic comparison is performed between the ITEC values (total electron content derived from ionograms) calculated from Athens Digisonde observations and TEC data derived for Athens coordinates from the TEC maps produced by the DLR/IKN for Europe, using GPS measurements. The first results of the comparison study performed between the two data sets shows that apart of the general daytime agreement, a systematic deviation of ITEC towards lower values during nighttime hours is present. Given the adequate accuracy of both independent measurements, the observed difference during nighttime could provide a measure of the plasmaspheric content wich is an open issue in both geomagnetically disturbed and undisturbed periods and further improve existing plasmaspheric models.