Types of Narrow Bipolar Pulse Wave Shapes Obtained With a Dense Array of Ground-Based E-change Sensors

Abstract:

Narrow bipolar pulses (NBPs) or compact intracloud discharges are considered compact, singular, high energy, and high altitude lightning events that have been studied for more than three decades. During summer of 2011, we operated ten stations of wide band (band width 0.16 Hz – 2.5 MHz) electric field change meters covering an area of nearly 70x100km² in and around Kennedy Space Center (KSC), Florida, USA. On 14 August 2011, we detected 245 positive polarity NBPs within 200 km of KSC. We identified characteristic variations of IBP wave forms in E-change data and categorized these into three main groups; Type A: clean NBPs (4.9%), Type B: NBPs with secondary peaks in the tail (27.5%), and Type C: NBPs with relatively fast rise time with a noisy fall/tail (14.3%). The majority (53.3%) of our NBPs could not be categorized into the above groups due to extra sub-pulses (noisiness) in the NBP waveforms. Therefore, we further categorize the remaining 53.3% NBPs into five other sub-groups according to where the extra noisiness occurred. Even though our waveform analysis does not suggest that these sub-groups are related to the main groups, power spectral density (PSD) curve analysis shows that each of these sub-groups has a similar PSD curve as one of the main groups. In this presentation, we will discuss these different types of NBPs and compare their physical properties including their altitudes (obtained by time of arrival method), isolation from other lightning activity, peak current estimations, RMS power radiation, and PSD curves.