Effect of ionospheric current system geometry on local surface EM observation - a theoretical model
Thursday, 26 May 2016
Istvan Lemperger1, Viktor Wesztergom1, Michel Menvielle2, Sándor Szalai1, Arpad Kis1, Attila Novák1, Ahmed Lethy3, Pál Bencze1 and Lukacs Benedek Kuslits1, (1)Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Sopron, Hungary, (2)LATMOS Laboratoire Atmosphères, Milieux, Observations Spatiales, Paris Cedex 05, France, (3)NRIAG, Helwan, Egypt
Abstract:
The primary natural source of the ULF range surface geomagnetic field variations are the ionospheric-magnetospheric currents. Subsurface electric (telluric) currents arise by means of the induction effect, resulting secondary magnetic field at the surface. The total surface geomagnetic field is superposition of the primary and the secondary components. The surface electromagnetic impedance is computed as the complex ratio of the telluric and total geomagnetic field at certain location of surface observation. The modulus and phase of the impedance tensor elements are dominantly determined by the spatial distribution of subsurface electric conductivity. However, the geometry of the source current systems might have significant indication on the impedance tensor at certain frequencies. In a theoretical approach, analytic computation of surface electromagnetic impedance has been performed in case of a general source current system geometry. Realistic ionospheric current system model and horizontal layered media have been assumed. The applied current system model is a temporally and spatially varying amplitude, 2D current density vector field in the height of 120km. The influence of the following parameters has been considered
- the parallel (with the current-density vector) extent of the source current system,
- the perpendicular (to the current-density vector) extent of the source current system ,
- the spatial variability of the source
- and the frequency.
above a physically realistic domain of the geometrical parameter-space. The presentation provides a brief summery of the results of the analytic calculations.
