Characteristics of electric fields of upward negative stepped leaders

We report simultaneous measurements of vertical electric fields and currents associated with positive flashes to the Säntis tower. The fields were measured at a distance of 14.7 km from the tower. All the data correspond to type-2 positive flashes characterized by currents with relatively slow rising portion on which oscillatory pulse trains, inferred to be due to an upward negative stepped leader, are superimposed. Bipolar electric field and current pulses associated with the upward negative stepped leader are examined and analyzed. The widths of the initial and second half cycles are found to be similar. The peak of the initial half cycle is found to be, on average, about twice as high as the peak of the second half cycle. A nearly linear correlation is found between the field peaks and associated current peaks.