Jun-Ichi Hojo

Measurement of horizontal electric fields associated with distant cloud‐to‐ground strokes

A broadband sensor for the horizontal component of the electric field associated with lightning discharges was developed. The vertical electric field component contaminating the output of this sensor was, on the average, only about 0.5% of the output. Simultaneous measurement of both vertical and horizontal electric field components, associated with lightning striking at more than 16 km away, confirms that the horizontal electric field is accurately evaluated from the measured vertical electric field with the help of the wave tilt formula, irrespective of the propagation path or the polarity of the cloud-to-ground stroke. From this simultaneous measurement, it is possible to estimate the effective conductivity and permittivity of the ground in the vicinity of the measuring site. These local electrical parameters are independent of those of the ground beneath the propagation path, which are estimated by comparing the attenuated electromagnetic waves propagated over land with relatively unattenuated electromagnetic waves propagated over seawater. The estimation becomes easier by measuring the horizontal electric field, as it is more sensitive to the attenuation.