Description of ionospheric disturbances observed by Vertical Ionospheric Sounding at 3 MHz

• Main Authors: James Arokiasami Baskaradas, Silvio Bianchi, Marco Pietrella, Michael Pezzopane, Umberto Sciacca, Enrico Zuccheretti
• Format: Article
• Language: English
• Published: Istituto Nazionale di Geofisica e Vulcanologia (INGV) 2014-03-01
• Series: Annals of Geophysics
• Subjects: Fading fluctuation; Ionospheric irregularities; Multipath fading; Ionograms
• Online Access: http://www.annalsofgeophysics.eu/index.php/annals/article/view/6345
• ISSN: 1593-5213; 2037-416X

<p>High Frequency radio waves reflected by the ionosphere can provide a relevant amount of information within the composite received signal. The ionosphere is indeed a frequency dispersive, bi-refractive, absorbing medium, in which multipath propagation occurs due to disturbance on a varied time-spatial scale. On the time-spatial level of Small Scale Disturbances (SSD) the ionosphere dynamics, detectable by Vertical Ionospheric Sounding (VIS), is mainly dependent on wrinkled layers acting as multi-reflectors. The present paper discusses different aspects of the effects of multipath fading suffered by the wave along the propagation path and potentially associated with SSD. To achieve these objectives, a VIS campaign at a fixed frequency of 3.0 MHz was conducted at the ionospheric observatory in Rome (Latitude 41.8 N; Longitude 12.5 E), by collecting a series of measurements of the power variations in received echo signals recorded between two consecutive ionograms whose sounding repetition rate was set to 15 min. The obtained results show that: 1) the fading suffered by the wave follows either a Rayleigh trend or a Nakagami-Rice trend, or a mix of them, the mixed case being the most frequent (about 65 % of the analysed cases); 2) the predominant periodicities characterizing the power variation are less than 25 s; such values are compatible with the small scale ionospheric disturbances; 3) for all the 24 hours of the day the ionospheric reflector is pretty stable and for time intervals of 10-30 s the periods of stability occur with a percentage of occurrence ranging between 55% and 95 %; for time intervals of 190- 210 s the periods of stability occur instead with a percentage of occurrence ranging between 5% and 54 %.</p>