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Pages 176-179

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From page 176...
... These 2 km normally contribute about SO percent to the total columnar resistance of around 1.3 X 10~7 Q m2 between sea level and the ionosphere. Direct measurements for the air-earth current density in the free atmosphere have been carried out also with long-wire antenna sondes described by Kasemir (19603.
From page 177...
... Here the electric-field strength near the ground shows a diurnal variation with universal time similar to that shown for the air-earth current density in Figure 12.17, both reflecting variations of the ionospheric potential. Over the continents consideration must be given to a varying ionization rate in the first few hundred meters caused by the exhalation of radioactive materials from the Earth.
From page 178...
... The reasons for the large variations at the disturbed stations are in both cases drifting pollution and/or space charges. Above the ground the vertical electric field Ez drops rapidly with increasing altitude owing to the increasing atmospheric conductivity.
From page 179...
... on the electric field near the ground (black station) compared with the electric field at the undisturbed station (Fischer, 1977)


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