Morphology of the spectral resonance structure of the electromagnetic background noise in the range of 0.1–4 Hz at <i>L</I> = 5.2

Abstract

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.

Detection of ionospheric Alfvén resonator signatures in the equatorial ionosphere

“…Additionally, the increase in Df is also steeper than IRI predictions, suggesting larger density gradients near the terminator, a conclusion also drawn for the D-region from observations onboard balloons for different solar activity [Simões et al, 2009[Simões et al, , 2011b. Discrepancies between IRI (specifically, IRI-95) and IAR ground measurements at high latitude during previous solar minimum have been noted; according to IAR measurements, IRI tends to overestimate plasma density, particularly above the F-peak and low solar activity [Yahnin et al, 2003]. Although the modifications introduced in IRI profiles -taking into account plasma density and composition as measured by C/NOFSprovide larger Df, additional corrections are necessary to IRI for fitting IAR results.…”

Automatic detection of ionospheric Alfvén resonances using signal and image processing techniques

“…This parameter can be used to determine length interval of the cavity if the corresponding foF2 values are available (e.g. Yahnin et al, 2003). From this other parameters such as the Alfvén velocity can be estimated.…”

“…Further theoretical models have been developed (e.g. Lysak, 1993;Bösinger et al, 2009) to explain the phenomenon, and experimental work has provided evidence for their occurrence at low (Bösinger et al, 2002), middle (Kulak et al, 1999;Hebden et al, 2005) and high latitudes (Belyaev et al, 1999;Yahnin et al, 2003;Molchanov et al, 2004) in the Northern Hemisphere. Other researchers have shown SRSs are present in the Southern Hemisphere; for example, Yaun (2011) investigated SRSs measured at Halley Bay in Antarctica.…”

Use of the International Reference Ionosphere 2012 model to calculate emission frequency scale of the ionospheric Alfvén resonator

“…Daily, seasonal, and cyclic variations in the properties of the IAR (Belyaev et al 1997;Yahnin et al 2003) were examined. Their relation to various geomagnetic and geophysical processes (Guglielmi et al 2006;Potapov et al 2008;Dovbnya et al 2010Dovbnya et al , 2012 and to the state of the ionosphere (Yahnin et al 2003;Hebden et al 2005;Parent et al 2010;Potapov et al 2014) was studied.…”

“…Daily, seasonal, and cyclic variations in the properties of the IAR (Belyaev et al 1997;Yahnin et al 2003) were examined. Their relation to various geomagnetic and geophysical processes (Guglielmi et al 2006;Potapov et al 2008;Dovbnya et al 2010Dovbnya et al , 2012 and to the state of the ionosphere (Yahnin et al 2003;Hebden et al 2005;Parent et al 2010;Potapov et al 2014) was studied. A number of authors made suggestions on using the observations of the electromagnetic emission spectral structure within the 0.5-10 Hz range for sounding the ionospheric parameters and specifying ionospheric models (Demekhov et al 2000;Yahnin et al 2003;Parent et al 2010).…”