  Seismo-ionosphere coupling processes have been investigated considering the
GPS observed anomalous ionospheric Total Electron Content (TEC) variations
before strong earthquakes as their precursors. The numerical simulations'
results of the TEC response on the vertical electric currents flowing between
the Earth and ionosphere during the earthquake (EQ) preparation time have been
performed. Model experiments have been carried out using the Upper Atmosphere
Model. The following currents' parameters were varied in: (i) direction (to or
from the ionosphere); (ii) latitudinal zone of the sources' (EQ epicenters)
location; (iii) currents' configuration: (1) grid nodes with "straight"
currents were surrounded by "border" grid points with currents of opposite
direction ("return" currents); (2) the "return" currents were spread out over
the globe; (3) without "return" currents. Numerical simulations have shown that
electric currents with density of 4\times10-8 A/m2 over the area of about 200
km in longitude and 2500 km in latitude produce both positive and negative TEC
disturbances with magnitude up to 35 % in agreement with GPS TEC observations
before EQs.
