Influences of the Presence of a Tall Grounded Strike Object and an Upward Connecting Leader on Lightning Currents and Electromagnetic Fields

Using a generalized transmission line model of the lightning return stroke, we have investigated the influences of the presence of a tall strike object and an upward connecting leader on the magnitude of lightning current and on associated electric and magnetic fields. For a typical subsequent lightning return stroke, the peak current at the bottom of a 100-m-high object is 1.5 times larger than the channel base peak current for the same strike to the flat ground, regardless of the presence of a 20-m-long upward connecting leader, while the lightning peak current at the top of the strike object is not much different from the current in the absence of the object. The vertical electric field due to a lightning strike to a 100-m-high object E_z-tall is reduced relative to that due to the same strike to the flat ground E_{z- flat} at distances ranging from 30 m to 200 m from the object and enhanced at distances greater than 200 m. The azimuthal magnetic field for the tall object case H_phi-tall is larger than that for the flat ground case H_phi-flatt at any distance. Beyond about 3 km, E_{z-tall /} E_{z- flat} becomes insensitive to distance change and is equal to H_{phi-tall /} H_phi-flatt.