Electrostatic field changes and durations of narrow bipolar events

Abstract

Using an array of 10 sensors, electric field change measurements of 35 positive narrow bipolar events (NBEs) were obtained at close range (≤10 km). At the closest sensor all 35 NBEs had a net electrostatic change (ΔEfast) associated with the main bipolar pulse with amplitudes of 0.4 to 16.3 V/m (not range normalized). At the closest sensor the bipolar pulse of each of the 35 NBEs was followed by a relatively long, slow electrostatic change (ΔEslow) with amplitudes of 0.1 to 43.4 V/m and durations of 0.7 to 33.7 ms. For ΔEfast, estimated 3‐D charge moments for 10 NBEs ranged from 0.46 C km to 1.81 C km with an average and standard deviation of (1.09 ± 0.36) C km. Seven 3‐D charge moments were essentially vertically oriented, and the other three moments were tilted at 10°–20° from vertical. The 10 3‐D charge moments were overlaid on vertical radar cross sections; 6 NBEs occurred in weak reflectivity near the upper reflectivity boundary; the other 4 NBEs occurred near the top of the high‐reflectivity core of the thunderclouds. For ΔEslow, we estimated 3‐D charge moments for only three NBEs; they ranged from 1.11 C km to 2.69 C km with an average of (1.83 ± 0.80) C km. A two current transmission line model matched the bipolar pulse and the following slow change (ΔEslow) of one NBE reasonably well. The slow change mechanism may be different from the NBE mechanism and similar to the initial E‐change before typical lightning flashes.

Modeling Compact Intracloud Discharge (CID) as a Streamer Burst

“…Note that the static field has a polarity opposite to that of the initial radiation field. This feature is in agreement with the experimental data presented in [39] and [40].…”

“…So far, we have studied the effect of various parameters of the streamer burst on the radiation field generated by CIDs. Not much information is available on the field signatures of CIDs measured close to their point of origin, but references [39] and [40] provide a few examples. These examples show the presence of a static field in the close signature of the NBP.…”

Initial electric field changes of lightning flashes in two thunderstorms

“…[] determined the average charge moment of 15 positive NBEs to be 380 C m with a range of 260–800 C m, and Karunarathne et al . [] found that the average charge moment of 10 positive NBEs measured within the reversal distance was 1090 C m with a range of 460–1810 C m. Rison et al . [] calculated the charge moments of three NBEs that initiated IC flashes and found them to be −80, −90, and −180 C m. Thus, the largest charge moments of FPBs that initiate IC flashes (namely, NBEs) can be substantially larger than the largest IEC charge moments measured herein.…”

“…[, Figures 2 and 3], and Karunarathne et al . []. Therefore, we identify the two IEC initiating pulses in Figure as NBE‐type pulses.…”

“…The range of FPB charge moments is unknown, but based on the Rison et al [2016] data, they must be much smaller than the charge moments of NBEs. Smith et al [1999] determined the average charge moment of 15 positive NBEs to be 380 C m with a range of 260-800 C m, and Karunarathne et al [2016] found that the average charge moment of 10 positive NBEs measured within the reversal distance was 1090 C m with a range of 460-1810 C m. Rison et al [2016] calculated the charge moments of three NBEs that initiated IC flashes and found them to be À80, À90, and À180 C m. Thus, the largest charge moments of FPBs that initiate IC flashes (namely, NBEs) can be substantially larger than the largest IEC charge moments measured herein. It now seems obvious that for the two storms studied herein, the charge moment of flash-initiating FPB was always insufficient to cause the first IB pulse, because each flash had (and therefore 'needed') an IEC to produce the first IB pulse.…”