Preparation of an advanced TEC forecast based on the statistical analysis of historical ionospheric storms

The forecast of ionospheric conditions and especially of the total electron content (TEC) disturbances is a challenging task and currently of major interest to the space weather community. Short term (up to one hour) forecasting of TEC under quiet geomagnetic conditions is practiced at a few institutions worldwide. However, a forecast of up to 24 hours and more is requested by users in order to identify and mitigate the impact on communication systems at the earliest possible date. Solar storm induced geomagnetic and ionospheric perturbations cause large errors in the forecast since measurements of the onset time, location of maximum perturbation, strength and type of storm deviate much from the climatology. Hence, ionospheric storms need first to be described by an appropriate model to ensure good forecast quality.\ The forecast of perturbed TEC is part of the Forecast System Ionosphere build under the umbrella of the FP7 project AFFECTS (Advanced Forecast For Ensuring Communication Through Space). We present the statistical analyses of numerous storm events observed in the TEC since 1995, which enables us to derive an empirical model to estimate and predict a most probable upcoming perturbed TEC over Europe. A crucial input to a forecast of perturbed TEC is the storm onset indicator. Therefore, we discuss a new storm onset definition based on ACE measurements