GPS/GLONASS-based TEC measurements - as a contributor for space weather forecast

Space weather monitoring and forecast require a permanent monitoring of the ionospheric state on global scale. The world-wide use of global navigation satellite systems such as GPS and GLONASS offers 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 study we turn our attention to TEC variations over the European area. Using the data of more than 15 GPS stations of the GPS tracking network of the International GPS Service (IGS), a horizontal resolution in the order of 500 kin is achieved, the standard time resolution is 10 min. The total ionization of the ionosphere reacts very sensitive to solar radiation changes. As correlation studies with the solar radio flux index F10.7 have shown, the ionospheric response over the European area is delayed by about 1-3 days depending on geophysical conditions. Consequently, the turn off/on of the solar radiation during the solar eclipse on August 11, 1999 was seen as a significant reduction of TEC following the obscuration function with a delay of up to 40 min. Ground-based GPS measurements can effectively be used for detecting large-scale horizontal structures and their motion (up to 30 s time resolution) during perturbation processes (see http://www.kn.nz.dlr.de/). These capabilities are demonstrated by analyzing individual storms of January 10, 1997 and of April 6, 2000. For the latter also TEC maps of the Northern polar cap down to 50degreesN were computed. These polar maps indicate strong ionization enhancements around the geomagnetic pole in the evening hours. Furthermore, simultaneous high rate sampled GPS and GLONASS data are presented that demonstrate the impact of perturbation-induced small-scale irregularities in the ionosphere on satellite signals in operational communication and navigation systems. (C) 2002 Elsevier Science Ltd. All rights reserved.