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

Abstract

Based on recent developments in the formalism governing the spectral resonance structures (SRS) of the Ionospheric Alfvén resonator (IAR) as observed on the Earth's surface, a numerical code was developed to investigate properties of SRS which can in particular be contributed to magnetic inclination effects. Among the theoretical findings are: 1) SRS is discernible in both orthogonal components, 2) the harmonic structure of SRS is not anymore over frequency equidistantly distributed, 3) the frequency scales of SRS differ in the two normal modes. The theoretically predicted properties could be found in the observations of a low latitude and some of them even in the data of a mid latitude station. The verification, however, is not as straight forward because the predicted effects do not only depend on magnetic inclination but also on the wave angle of the lightning induced electromagnetic wave k-vector with the normal to the magnetic meridian passing through the observation site. So far the formalism is simplified as it deals with a single source situation alone whereas the actual observation is a composite of excitations caused by an average of about 60 flashes of lightning operating all the time, world-wide. © Author(s) 2009.