Research Article

Solar radio emission as a disturbance of aeronautical radionavigation

¹ Solar-Terrestrial Center of Excellence – SIDC, Royal Observatory of Belgium, Avenue Circulaire 3, 1180 Brussels, Belgium
² LESIA-UMR 8109 and Station de radioastronomie de Nançay – Observatoire de Paris, CNRS (further affiliations: PSL Res. Univ., Univ. P & M Curie and Paris-Diderot, University of Orléans, OSUC), 92190 Meudon, France
³ Institute for Particle Physics and Astrophysics, ETH Zürich, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland
⁴ Swedish Institute of Space Physics, Box 537, 75121 Uppsala, Sweden
⁵ Goddard Space Flight Center Greenbelt, MD, USA
⁶ University of Applied Sciences and Arts Northwestern Switzerland, Windisch, Switzerland
⁷ Belgocontrol, Tervuursesteenweg 303, 1820 Steenokkerzeel, Belgium
⁸ Air Greenland – Engineering Department, P.O. Box 1012, Nuuk, Greenland

^* Corresponding author: christophe.marque@oma.be

Received: 28 September 2017
Accepted: 6 August 2018

Abstract

On November 4th, 2015 secondary air traffic control radar was strongly disturbed in Sweden and some other European countries. The disturbances occurred when the radar antennas were pointing at the Sun. In this paper, we show that the disturbances coincided with the time of peaks of an exceptionally strong (∼10⁵ Solar Flux Units) solar radio burst in a relatively narrow frequency range around 1 GHz. This indicates that this radio burst is the most probable space weather candidate for explaining the radar disturbances. The dynamic radio spectrum shows that the high flux densities are not due to synchrotron emission of energetic electrons, but to coherent emission processes, which produce a large variety of rapidly varying short bursts (such as pulsations, fiber bursts, and zebra patterns). The radio burst occurs outside the impulsive phase of the associated flare, about 30 min after the soft X-ray peak, and it is temporarily associated with fast evolving activity occurring in strong solar magnetic fields. While the relationship with strong magnetic fields and the coherent spectral nature of the radio burst provide hints towards the physical processes which generate such disturbances, we have so far no means to forecast them. Well-calibrated monitoring instruments of whole Sun radio fluxes covering the UHF band could at least provide a real-time identification of the origin of such disturbances, which reports in the literature show to also affect GPS signal reception.