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Morphology of the spectral resonance structure of the electromagnetic background noise in the range of 0.1–4 Hz at L = 5.2

Morphology of the spectral resonance structure of the electromagnetic background noise in the range of 0.1–4 Hz at L = 5.2

Authors :
A. A. Ostapenko
Tauno Turunen
Jyrki Manninen
J. Kangas
Nadezhda V. Semenova
A. G. Yahnin
Source :
Annales Geophysicae. 21:779-786
Publication Year :
2003
Publisher :
Copernicus GmbH, 2003.

Abstract

Continuous observations of fluctuations of the geomagnetic field at Sodankylä Geophysical Observatory (L = 5.2) were used for a comprehensive morphological study of the spectral resonance structure (SRS) seen in the background electromagnetic noise in the frequency range of 0.1–4.0 Hz. It is shown that the occurrence rate of SRS is higher in the nighttime than in the daytime. The occurrence rate is higher in winter than in summer. The SRS frequencies and the difference between neighbouring eigenfrequencies (the frequency scale) increase towards nighttime and decrease towards daytime. Both frequency scale and occurrence rate exhibit a clear tendency to decrease from minimum to maximum of the solar activity cycle. It is found that the occurrence rate of SRS decreases when geomagnetic activity increases. The SRS is believed to be a consequence of a resonator for Alfvén waves, which is suggested to exist in the upper ionosphere. According to the theory of the ionospheric Alfvén resonator (IAR), characteristics of SRS crucially depend on electron density in the F-layer maximum, as well as on the altitudinal scale of the density decay above the maximum.We compared the SRS morphological properties with predictions of the IAR theory. The ionospheric parameters needed for calculation were obtained from the ionosphere model (IRI-95), as well as from measurements made with the ionosonde in Sodankylä. We conclude that, indeed, the main morphological properties of SRS are explained on the basis of the IAR theory. The measured parameters of SRS can be used for improving the ionospheric models.Key words. Ionosphere (auroral ionosphere; wave propagation) – Radio Science (electromagnetic noise and interference)

Details

ISSN :
14320576
Volume :
21
Database :
OpenAIRE
Journal :
Annales Geophysicae
Accession number :
edsair.doi...........6b3a28023884f8269490cb4f38f9326a
Full Text :
https://doi.org/10.5194/angeo-21-779-2003