Abstract
Travelling Ionospheric Disturbances (TIDs) constitute an important Space Weather effect in the upper atmosphere driven by the near-Earth space dynamics and by lower atmosphere phenomena. TIDs are the ionospheric manifestation of internal atmospheric gravity waves (AGW) in the neutral atmosphere. Independent of their source, the effects imposed by TIDs at the ionospheric altitudes are very important, as they can impose disturbances with amplitudes of up to ~20% of the ambient electron density, and a Doppler frequency shifts of the order of 0.5 Hz on HF signals. Because TIDs affect all technologies using predictable ionospheric characteristics, a comprehensive system for the direct and accurate identification and tracking of TIDs is the cornerstone for the development of mitigation strategies that will support the reliable and safe operation of the systems affected. This requires (a) the real-time calculation of the TID characteristics (velocity, amplitude, propagation direction) (b) the accurate specification of all disturbances that act in the ionosphere and create the prevailing ionospheric conditions, (c) the specification of those ionospheric characteristics whose perturbation, because of TIDs, cause the impact in each specific technology. The talk reviews the most well-known methodologies for the identification and tracking of TIDs based on the exploitation of real-time observations from networks of Digisonde, GNSS receivers and Continuous Doppler Sounding Systems. Activities planned by the ionospheric community for the development of a warning system able to support the development of mitigation technologies will be also presented. These activities are part of the newly funded EC Horizon 2020 Project TechTIDE which is expected to start in November 2017.