TITLE:
A Study on the Influence of Solar Flares on High Frequency Radio Propagation
AUTHORS:
Khoder Khaled, Ahmad El Sayed Ahmad, Pascal Pagani, Rolland Fleury
KEYWORDS:
Solar Flare, X-ray Flux, Ionosphere, HF Propagation, Sudden Ionospheric Disturbance, Broadcast Transmitters
JOURNAL NAME:
Open Journal of Antennas and Propagation,
Vol.13 No.2,
October
14,
2025
ABSTRACT: On 25 October 2013, the Sun emitted two significant solar flares. The first solar flare, classified X1.7, peaked at 08:01 UT. The second one, X2.1, peaked at 15:03 UT and was accompanied by solar radio emission. In this work, we study the ionospheric response to the two X‐class solar flares and their impact on high‐frequency (HF) propagation. For this aim, opportunistic HF signals are used; these signals correspond to any HF communication signal using the ionospheric channel as a transmission medium. First, an identification procedure of opportunistic HF radio waves is presented using measurements performed in the cities of Toulon, France (43.11˚N; 5.93˚E) and Brest, France (48.40˚N; 4.48˚W). Among several identified HF transmitters, those which are in operation during the two solar flares are selected. In the second part, we present some information confirming the detection of two solar flares on 25 October and study their effects on HF signals received in France.