Observations of positive narrow bipolar pulses

Abstract

AbstractWaveforms of 226 positive narrow bipolar pulses (NBPs) were obtained with five to eight stations of E‐change meters covering an area of 70 × 100 km2. The NBPs had typical average parameters: 10–90% rise time of 2.6 μs, full width at half maximum time of 2.8 μs, zero cross time of 9.9 μs, and range‐normalized amplitude at 100 km of 11.0 V/m. Four main types of positive NBP waveforms were identified: Type A had a simple bipolar waveform with a positive peak and a negative overshoot peak (1% of NBPs), Type B had extra peak(s) superimposed on the overshoot peak (67%), Type C had extra peak(s) on or just after the main positive peak (13%), and Type D had extra peak(s) before the main positive peak (19%). Regardless of type, each NBP waveform maintained its basic shape across a range of 10 to 130 km from its origin. NBP locations, obtained with a time of arrival technique, seemed unrestricted in their horizontal distribution (except for Type C), while NBP altitudes ranged from 7 to 19 km with an average of 13 km. Estimated peak currents were 2–126 kA with an average of 30 kA. Isolation of NBPs from other lightning events was determined for both temporal (660 ms) and spatial (>10 km) quantities; 37% of NBPs were isolated, 38% occurred within 660 ms before a flash, 19% occurred within flashes, and 11% occurred within 660 ms after a flash. The total RMS power radiated by NBPs within 1 kHz–2.5 MHz bandwidth had a range of 5.0 × 106–6.1 × 108 W with an average of 7.8 × 107 W.