Positive lightning: An overview, new observations, and inferences

Abstract

[1] We examine the various conceptual cloud charge configurations and scenarios leading to production of positive lightning with a view toward an explanation of its observed properties. Data for 52 positive cloud-to-ground flashes containing 63 strokes recorded in Gainesville, Florida, in 2007 are presented and discussed. The U.S. National Lightning Detection Network (NLDN) located 51 (96%) of the positive strokes at distances of 7.8 to 157 km from the field-measuring station. In 42 (81%) of the 52 flashes, the first (or the only) leader-return stroke sequence was not preceded by in-cloud discharge activity. The average number of strokes per flash is 1.2. Single-stroke flashes constitute 81%. In three (38%) of eight two-stroke flashes, the second stroke likely followed the channel of the first stroke, and in five (62%) flashes it likely created a new termination on ground. Eight (15%) of the 52 positive flashes had detectable preliminary breakdown pulse trains in their electric field records. Electric field waveforms of 14 (27%) first strokes (also of one third stroke) are preceded by pronounced pulses, apparently indicative of leader stepping. NLDN-reported peak currents for 48 positive strokes in 40 flashes ranged from 20 to 234 kA with a geometric mean value of 75 kA. The median charge transfers in 1, 2, and 40 ms after the beginning of return stroke electric field change for an assumed height of 12 km were estimated to be 13, 18, and 34 C, respectively. Two bipolar lightning discharges are additionally examined.

Characterization of Positive Cloud to Ground Flashes Observed in Indonesia

“…However, positive lightning flashes may lead to more damage to electric power and telecommunication systems than negative lightning flashes. Further, they have properties that are different from those of negative lightning flashes, such as high peak current, and differences in the number of strokes per flash, continuing current, charge transfer, leader propagation, and branch patterns [2][3][4][5]. Generally, a downward leader has many branches.…”

O bserved Electric Field Changes o f Positive Lightning Flashes Preceded b y Preliminary Breakdown i n Padang

“…This indicates that the position of the negative charge under a main positive charge center of a thundercloud producing type S is dominant in positive CG flashes in Padang. According to Nag et al [2], an inverted dipole with a lower negative charge (LNC) may lead to an electric field change of positive lightning with such a charge configuration. Our dominant type percentage of PB pulse trains is similar to that of Gomez and Cooray [9], found at a higher latitude.…”

“…They may lead to more damage to grounded objects than negative lightning. They are often related to severe weather that produces phenomena such as heavy rain, strong winds and large hail storms [2]. Furthermore, they also have properties that are different from those of negative lightning flashes, such as preliminary (initial) breakdown, leader propagation and high peak current [2][3][4][5].…”

“…It has been found that in positive ground flashes, the initial pulse polarity of the electric field that is preceded by the PB process is sometimes different from that of the following RS [6][7][8][9][10]. The initiating mechanism of the positive lightning discharge remains a mystery because the charge structure of thunderclouds that create positive lightning is more complex than in the case of negative lightning [1,2,11,12]. In addition, only few studies have been reported about lightning flashes in tropical regions compared to temperate regions [13][14].…”

Features of Ground Flashes before and after the Massive Earthquake Observed from Kathmandu, Nepal

“…However, the charge structure of the cloud still remains a mystery. Because of the paucity of their occurrence, positive ground flashes are considerably less studied and hence less understood as compared to their negative counterparts (Nag and Rakov, 2012). According to Williams (1989), the lightning activity itself follows a specific pattern with the intracloud (IC) lightning normally appearing in the developing stage followed by the cloud-to-ground (CG) lightning during the mature stage, whereas, both types of lightning can occur in the decaying stage of thunderstorms.…”