Top-down and Bottom-up Coupling between Ionosphere and Solid Earth (Invited)

Widely reported ionospheric perturbations above epicentral regions prior to major earthquakes suggest an upward coupling, reaching from the ground to the ionosphere [1]. Conversely, seismic activity has been shown to be correlated to the Sq values and, hence, to the plasma density in the ionosphere, which is driven by the sun’s activity [2]. This suggests a top-down coupling of the ionosphere into the Earth’s crust. Laboratory observations of massive air ionization at the rock-to-air interface [3] and field observations of bursts of high air ion concentrations [4, 5], lasting typically 6-24 hrs, provide an interesting hint as to how to the bottom-up coupling may work. It is hypothesized that, as air “bubbles” laden with positive ions, expand upward into the stratosphere, they drag along the Earth’s ground potential. This causes a redistribution of the Total Electron Concentration, TEC, in the ionosphere above the epicentral region. The top-down coupling can be explained by two coupling mechanisms operating during the passage of every point on the surface of the Earth under the leading and the trailing edges of the ionospheric current vortices: (i) Lorentz forces resulting from the telluric currents that are induced in the Earth’s crust, and (ii) the Einstein-DeHaas effect resulting from the interaction of magnetic field changes with paramagnetic ions in the crust. [1] Liu et al.: A statistical investigation of pre-earthquake ionospheric anomaly, J. Geophys. Res. 111, A05304 (2006). [2] Duma and Ruzhin: Diurnal changes of earthquake activity and geomagnetic Sq-variations, Nat. Hazards Earth System Sci. 3, 171-177 (2003). [3] Freund et al.: Air ionization at rock surface and pre-earthquake signals, J. Atmos. Sol. Terr. Phys. 71, 1824-1834 (2009). [4] http://www.e-pisco.jp/ [5] Bleier et al.: Investigation of ULF magnetic pulsations, air conductivity changes, and infrared signatures associated with the 30 October 2007 Alum Rock M5.4 earthquake, Nat. Hazards Earth Syst. Sci., 9, 585-603 (2009).