Abstract
Traveling Ionospheric Disturbances (TIDs) reflect changes in the ionospheric electron density which are caused by atmospheric gravity waves. These changes in the electron density impact the functionality of different applications such as precise navigation and high-frequency geolocation. The Horizon 2020 project TechTIDE establishes a warning system for the occurrence of TIDs with the motivation to mitigate their impact on communication and navigation applications. This requires the identification of appropriate indicators for the generation of TIDs and for this purpose we investigate potential precursors for the TID occurrence. This paper presents a case study of the double main phase geomagnetic storm, starting from the night of 7th September and lasting until the end of 8th September 2017. Detrended Total Electron Content (TEC) derived from Global Navigation Satellite System (GNSS) measurements from more than 880 ground stations in Europe was used to identify the occurrence of different types of large scale traveling ionospheric disturbances (LSTIDs) propagating over the European sector. In this case study, LSTIDs were observed more frequently and with higher amplitude during periods of enhanced auroral activity, as indicated by increased electrojet index (IE) from the International Monitor for Auroral Geomagnetic Effects (IMAGE). Our investigation suggests that Joule heating due to the dissipation of Pedersen currents is the main contributor to the excitation of the observed LSTIDs. We observe that the LSTIDs are excited predominantly after strong ionospheric perturbations at high-latitudes. Ionospheric parameters including TEC gradients, the Along Arc TEC Rate (AATR) index and the Rate Of change of TEC index (ROTI) have been analysed for their suitability to serve as a precursor for LSTID occurrence in mid-latitude Europe, aiming for near real-time indication and warning of LSTID activity. The results of the presented case study suggest that the AATR index and TEC gradients are promising candidates for near real-time indication and warning of the LSTIDs occurrence in mid-latitude Europe since they have a close relation to the source mechanisms of LSTIDs during periods of increased auroral activity.
Highlights
Geomagnetic storms and their associated effects have been intensively investigated for decades in order to better understand the phenomena, and to measure their impact on human technologies (Gonzales et al, 1994)
We analyze in a case study the ionospheric perturbations which occur in the source region of large scale traveling ionospheric disturbances (LSTIDs), targeting the following two objectives: 1. Identification of individual ionospheric perturbation indices that can serve as precursors for the LSTIDs occurrence in the mid-latitude European region
We present the procedure used for the LSTIDs detection, the potential precursors investigated in this work (AATR, Rate Of change of TEC index (ROTI) and Total Electron Content (TEC) gradients), along with the measurements and indices used to support the analysis of the ionosphere-thermosphere dynamics that contributed to the excitation of LSTIDs
Summary
Geomagnetic storms and their associated effects have been intensively investigated for decades in order to better understand the phenomena, and to measure their impact on human technologies (Gonzales et al, 1994). These storms are closely related to ionospheric perturbations, such as significant. LSTIDs propagate with horizontal velocities between 400 and 1000 m/s, horizontal wavelengths greater than 1000 km and periods in the range of 30 min to 3 h (Hunsucker, 1982; Hocke & Schlegel, 1996) Another type of TIDs are the medium-scale TIDs (MSTIDs), which propagate with velocities between 100 and 250 m/s, periods in the range of 10 min to 1 h and wavelengths between 100 and 1000 km (Hunsucker, 1982; Shiokawa et al, 2009; Chum & Podolská, 2018). Mid-latitude MSTIDs are considered to be excited by diverse mechanisms (see Kotake et al, 2006, 2007; Kelley, 2011; Otsuka et al, 2013; Chen et al, 2019) and are out of the scope of this work
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