A quantitative analysis of the diurnal evolution of Ionospheric Alfvén resonator magnetic resonance features and calculation of changing IAR parameters

Abstract

Abstract. Resonance features of the Ionospheric AlfvénResonator (IAR) can be observed in pulsation magnetometer data from Sodankylä, Finland using dynamic spectra visualizations. IAR resonance features were identified on 13 of 30 days in October 1998, with resonance structures lasting for 3 or more hours over 10 intervals. The diurnal evolution of the harmonic features was quantified for these 10 intervals using a manual cursor-clicking technique. The resonance features displayed strong linear relationships between harmonic frequency and harmonic number for all of the time intervals studied, enabling a homogeneous cavity model for the IAR to be adopted to interpret the data. This enabled the diurnal variation of the effective size of the IAR to be obtained for each of the 10 time intervals. The average effective size was found to be 530 km, and to have an average variation of 32% over each time interval: small compared to the average variation in Alfvén velocity of 61%. Thus the diurnal variation of the harmonics is chiefly caused by the changing plasma density within the IAR due to changing insolation. This study confirms Odzimek (2004) that the dominating factor affecting the IAR eigenfrequencies is the variation in the Alfvén velocity at the F-layer ion-density peak, with the changing IAR size affecting the IAR eigenfrequencies to a smaller extent. Another IAR parameter was derived from the analysis of the IAR resonance features associated with the phase matching structure of the standing waves in the IAR. This parameter varied over the time intervals studied by 20% on average, possibly due to changing ionospheric conductivity.

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

“…But sometimes the WKB approach gives satisfactory results for wavelengths comparable with the system size. In case of the IAR emission, we have long wavelengths for low harmonics, but the space between the harmonics is almost constant for all harmonics, as one can see from Figure 2 (see also Hebden et al 2005). This is a sign indicating that in this particular case the WKB can be applied, at least as a zero approximation.…”

“…The frequency scale Df values were measured on spectrograms by using a manual on-screen cursor clicking technique for each pair of the adjacent bands opposite every hour mark given that the spectral bands (harmonics) of IAR emission were evident for that hour. (A similar technique was used in Hebden et al 2005.) Then, the Df values measured between different harmonic pairs were averaged providing one Df value for each hour.…”

“…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).…”

On the coupling of fast and shear Alfvén wave modes by the ionospheric Hall conductance

“…As an example, Hebden et al (2005) observed harmonics up to almost 5 Hz from magnetometer data obtained from Sodankylä, Finland. These observations can be modeled using the equations in a tilted magnetic field geometry such as those introduced by Sciffer and Waters (2002).…”

Magnetic-inclination effects in the spectral resonance structure of the ionospheric Alfvén resonator

“…Bösinger et al, 2002;Semenova and Yahnin, 2008), usage in ionospheric diagnostics (e.g. Hebden et al, 2005;Odzimek et al, 2006), IAR's role in atmospheric, ionospheric, magnetospheric coupling (e.g. Lysak, 1993;Demekhov et al, 2000;Bösinger and Shalimov, 2008), non-linear effects (e.g.…”