VERTICAL AND RADIAL ELECTRIC FIELDS FROM LEADERS AND RETURN STROKES ASSOCIATED WITH LIGHTNING STRIKES TO THE GAISBERG TOWER

We present and discuss measurements of electric fields (vertical and radial) from leaders and return strokes associated with lightning strikes to the Austrian Gaisberg Tower (GBT) obtained in 2008. The fields were measured at a distance of about 20 m from the tower. Simultaneously with the fields, return-stroke currents were also measured at the top of the tower. The vertical electric field waveforms appeared as asymmetrical V-shaped pulses. The initial, relatively slow, negative electric field change is due to the downward leader and the ensuing fast positive field change is due to the upward return stroke phase of the lightning discharge. The horizontal (radial) electric field due to the leader phase has a similar waveshape to the vertical electric field. However, the radial field due to the return stroke is characterized by a short negative pulse of the order of 1 microsecond or so, starting with a fast negative excursion followed by a positive one.