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  • Author or Editor: N Jakowski x
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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.

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Investigated is the relationship between the level of geomagnetic activity and the GPS TEC relative deviations from the monthly medians. Detailed information on this dependence is of crucial importance for developing a new synthetic index which, by quantifying the local response of TEC to geomagnetic activity, will be able to improve the quality of autocorrelation forecast procedures.</o:p>

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The GPS-derived TEC has proved to be a robust characteristic representing well the state of the Earth's ionosphere-plasmasphere system during both quiet and disturbed geomagnetic conditions. Successfully forecasting the TEC value can prove invaluable when trying to improve the communications, navigation, and surveying practices. Presented is a new forecasting method based on  auto-correlation analysis and consisting of two major parts - first, extrapolation of the TEC monthly medians using Fourier series approximation, and second, geomagnetically-correlated forecast of the TEC relative deviations of from its median value. Preliminary tests show a good agreement between measured and predicted median values. Presented are also important investigations related to the short-term forecast.

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The ionosphere region plays an active role in the complex space weather relationships. So a permanent monitoring of the ionospheric state on global scale is required. The world-wide use of Global Navigation Satellite Systems (GNSS) such as GPS and GLONASS offer the unique chance for a permanent monitoring of the total ionization (Total Electron Content -- TEC) of the global ionosphere/plasmasphere up to about 20000 km height.  In this paper we focus on space weather phenomena on 6--7 April 2000 in the ionosphere based on GPS, GLONASS and ionosonde measurements over Europe and over the northern polar cap. Depending on the density of the actual ground station distribution the horizontal resolution of the derived TEC maps is in the order of 500--1000 km. While discussing the special space weather event on 6--7 April 2000 it will be shown that TEC is very sensitive to perturbation induced dynamic forces such as particle precipitation, electric fields and meridional thermospheric winds. We suppose that the strong impact on the magnetosphere/ionosphere systems is due to the southward direction of the interplanetary magnetic field in the evening hours of 6 April. The ionosphere impact on navigation signals is demonstrated by analyzing 1Hz sampled data of GPS and GLONASS satellites. The derived signal phase irregularities due to ionospheric irregularities that degrade navigation and positioning applications indicate highly variable horizontal  structures.

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The radio limb sounding or occultation technique is capable of deriving accurate vertical profiles of atmospheric refractivity. This has been shown by very promising results of the first active GPS limb sounding GPS/MET experiment on Microlab 1. In this paper we report early results of ionospheric radio occultation (IRO) measurements carried out onboard the German satellite mission CHAMP (CHAllenging Minisatellite Payload) that contributes also to essential improvements of gravity and magnetic field models of the Earth.  First radio occultation measurements of the ionosphere were carried out by CHAMP on 11 April 2001.  Fortunately, ionospheric radio occultation measurements were switched on during the High Rate GPS/GLONASS  measuring campaign (HIRAC) initiated by the International GPS Service (IGS) and supported by COST 271 activities. So a comprehensive analysis of coordinated measurements will be possible within COST 271 cooperation in the near future.  The achieved accuracy of the retrieved electron density profiles is estimated by comparing them with independent ionosonde data.

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