1. Quantifying ionospheric disturbances for user oriented applications
I. Tsagouri, A. Belehaki, K. Koutroumbas and I. Xenaki
National Observatory of Athens, IAASARS, Greece
VarSITI Closing Symposium
June 10-14, 2019, Sofia, Bulgaria

2. Motivation
TechTIDE: Warning and Mitigation Technologies for TID (Travelling Ionospheric Disturbances) Effects (
Development of algorithms for the calculation of the ambient electron density and relevant key ionospheric characteristics (e.g. foF2, hmF2, TEC).
The ionospheric background will be used by the user to evaluate the criticality of current conditions.
Subtask 1: Develop algorithms for the efficient background representation. The algorithms should be able to: i. reproduce the normal ionospheric changes (e.g., diurnal, monthly, seasonal and solar cycle dependence), but also large scale variations (e.g., large scale storm time effects); ii. provide output in real-time.
Subtask 2: Address additional challenges in the monitoring of the ionospheric variation, including data quality issues and the characterization of the ionospheric disturbance level (weak, moderate, intense) for users’ needs.

3. Users’ groups Operations affected by ionospheric disturbances:
Systems using the ionosphere as part of their operations such as HF communication, HF geolocation operations
Systems for which the ionosphere is a noise, such as ground and space-based augmentation systems (EGNOS and GBAS)
After Goodman, 2005

4. Background representation (I)
Large scale storm effects:
Use of the 30-day running medians to determine the background conditions. This option is close to the concept of the monthly median that is used widely for the determination of the normal ionospheric variation in ionospheric studies, but available in real time at the same time. Indeed, comparison tests between 30-days running medians and monthly medians indicate that there is a satisfactory agreement between them within the uncertainty limits.

5. Background representation (II)
Small scale storm effects:
Use the 60 min running averages to determine the background conditions.
Bottom: The residuals of foF2 from their running median values (blue line) plotted together with the de-trended foF2 using the 60 min running averages as background (red line) over Dourbes. It is obvious that the two quantities differ largely since the de-trended foF2 does not include large scale ionospheric variations.

6. Characterization of the ionospheric activity level
1st step: Defining a threshold for significant disturbances.
In case of running medians, we use the relative standard deviation, STD (%) of the values taken into account in the calculation of the medians.
STD (%)=(STD_foF2 run median/foF2 run median)*100
The STD (%) is calculated in each epoch and it is depended on the characteristic, location, season and local time.
2012
7 locations
After Tsagouri et al., 2018

7. Characterization of the ionospheric activity level
dfoF2 median = [(foF2 – foF2_median)/foF2_median]*100

8. Characterization of the ionospheric activity level
dfoF2 median = [(foF2 – foF2_median)/foF2_median]*100
STD (%)=(STD_foF2 run median/foF2 run median)*100
Significant Disturbances

9. Characterization of the ionospheric activity level
Significant Disturbances

10. Example event: 7 - 10 September 2017 Overview of the activity
Geoeffective AR2673 emitted a series of solar flares, including:
an M5.5 at 20:33 UTC on Sept. 4;
an X2.2 at 9:10 UTC on Sept. 6 – the most prolonged flare of Solar Cycle 24;
an X9.3 at 12:02 UTC on Sept. 6 – the strongest flare of Solar Cycle 24;
Occurrence of an intense and multi-step geomagnetic storm (on September 7 -9) due to the combined effects of coronal mass ejections (CMEs) and High Speed Streams (HSSs).
1st excursion: 6 September 23:05 UTC
2nd excursion: 7 September 22:27 UTC
3rd excursion: 8 September 11:05 UTC
After Qian et al., 2018

11. TechTIDE activity report: AATR (Along Track TEC Rate) indicator of the ionospheric activity
The AATR time series for 4 European receivers.
7-8 September 2017
Linked to the increases in the geomagnetic activity, the AATR in the auroral region reaches values larger than 1TECU/min (indicative of strong ionospheric activity), while large AATR values are also for mid/high latitudes.
8 September 2017
Apart from the high ionospheric activity at high latitudes, it appears also some weak activity in the mid/high latitudes probably linked to a LSTID that propagates southwards from the auroral region.

12. TechTIDE activity report: HF Interferometry method performance
7 September 2017
8 September 2017
Europe
7 September 2017: LSTIDs with southward propagation occurring in the day-time and in the evening to mid-night hours.
8 September 2017: LSTID activity in the early hours of the day (until 2:00 UT) for all the European stations.
Typical characteristics of LSTIDs whose origin might be auroral.

13. TechTIDE activity report: HF - TID method performance
Europe, September 8:
Strong TID activity in the early morning and daytime hours.
September 7:
Strong TID activity in the evening hours.

14. TechTIDE activity report
Technological systems’ malfunctions:
Extended period of HF communication problems over Europe from 2100UT 7 September until 1400UT 9 September 2017: MUF drops and renders previously available link paths unusable (Frissell et al. 2019) – negative storm phase.
Degraded EGNOS performance on 8 September 2017 (Magdaleno et al. 2019)

15. Future plans
Systematic assessment of technological systems’ malfunctions wrt the intensity of the disturbances to fine tune the activity level (e.g. weak, moderate, intense – green, yellow, red).
The AATR index may be exploited for correlation studies, as it is well correlated to EGNOS degradation events

16. VarSITI Closing Symposium
Acknowledgments
We acknowledge support by:
EC Horizon 2020 project TechTIDE “Warning and Mitigation Technologies for Travelling Ionospheric Disturbances Effects”
“PROTEAS II” (MIS ) project, implemented under the Action “Reinforcement of the Research and Innovation Infrastructure”, funded by the Operational Programme “Competitiveness, Entrepreneurship and Innovation” (NSRF ) and co-financed by Greece and the European Union (European Regional Development Fund).
VarSITI Closing Symposium
June 10-14, 2019, Sofia, Bulgaria