Early Warning of ionospheric disturbances for GNSS users

Kurzfassung

Temporal and spatial gradients in the ionosphere can cause major threats on communication and navigation satellite systems, because the propagation of transionospheric radio signals is influenced by the ionospheric electron content. Space weather events are often the source of strong ionospheric disturbances. Forecasting ionospheric perturbations related to space weather events is therefore a crucial task being of special interest for GNSS users. The climatology of ionospheric storms seen in the Total Electron Content (TEC) over Europe as a response of the ionosphere towards Earth oriented space weather events is well known. It depends on season, elapsed time from event arrival, location and local time. However, the deviation of a single storm to the mean behavior can be large. A good correlation between strength of the ionospheric storm, i.e. the maximum deviation of the TEC to 27 day median, to solar wind or geomagnetic activity indices is hard to define. Hence forecasting TEC for disturbed conditions is a challenging task. However, the storm climatology and comprehensive correlation studies allow forecasting of the most probable TEC perturbation amplitude for the European region. GNSS users are in need of information about arriving threads due to space weather events as early as possible. Therefore, an Early Warning message for GNSS users has been developed at the DLR within the FP7-Project AFFECTS. It provides information about Earth endangering space weather events to interested GNSS users up to two days before their arrival. Additional information are now added by a second warning message distributed thirty minutes before arrival at Earth giving more specific information like exact arrival time, forecasts of geomagnetic indices, approximate TEC perturbation and range error for the European region. An overview on the Early Warning for GNSS user service provided by DLR is presented in this paper.