Therefore, the knowledge of the distinct electric characteristics of the battery cells is mandatory.
Several methods have been developed for this task (e.g. Pirjola, 2002; Pulkkinen et al., 2003a; Viljanen et al., 2004; McKay and Whaler, 2006; Thomson et al., 2009 and references therein), but they require some knowledge of the Earth's electric conductivity as input (typically 1D conductivity model or the regional impedance tensor that connects horizontal magnetic and electric disturbances).
These relationships, along with more detailed knowledge of the electrodynamics (currents, electric fields, and conductivities), lead to MHD model constraints.
However, our knowledge of the generation of electric fields in these configurations still remains incomplete, and this makes it difficult to understand the relationship between magnetic reconnection and the acceleration of energetic particles.
Knowledge of the resulting induced electric field at the Earth's surface is needed e.g. in modeling Geomag-netically Induced Currents (GIC) that flow in man-made conductor systems, such as gas and oil pipelines or highvoltage power grids (e.g. Pirjola, 2002).
Knowledge of the value of the electric field at a point, without any specific knowledge of what produced the field, is all that is needed to determine what will happen to electric charges close to that particular point.
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We have demonstrated that it is possible to estimate the geomagnetically induced electric field at the Earth's surface directly from the time derivative of the vertical magnetic field, without any knowledge of the underlying ground's electric conductivity.
