Evolution of lightning and the possible initiation/triggering of lightning discharges by the lower positive charge center in an isolated thundercloud in the tropics

Abstract

[1] The evolution of lightning and the shape of recovery curves after multiple-discharge flashes in a thundercloud have been studied from the surface measurements of electric field and Maxwell current near a tropical thundercloud. Observations suggest a tripole structure of the cloud and that its lower positive charge center (LPCC) plays a dominant role in initiating/triggering an intracloud (IC) or cloud-to-ground (CG) lightning discharge. IC discharges in the initial stage of thundercloud are followed by CG discharges from the LPCC and then by two distinct groups of multiple-discharge flashes. Each flash in the first group consists of an IC discharge triggered by a CG discharge and in the second group a CG discharge triggered by an IC discharge. Flashes in each group are bunched together for $15-20 min and occur with almost a regular periodicity of 1-1.5 min. The Maxwell current during every such flash in both groups has a bipolar transient and a positive overshoot that subsequently relaxes back to its predischarge value. The magnitudes of overshoot for the flashes in the first group are found to be much lower than those for the flashes in the second group. From a small portion of the recovery curves of such multiple-discharge flashes, one can conclude that the rate of charge buildup in the main negative charge center is higher than that in the LPCC.

Effects of the Inductive Charging on the Electrification and Lightning Discharges in Thunderstorms

“…8b and d) and the negative CG lightning initiation point height is between 4 -6 km. -CG flashes begin between the main negative charge and lower positive charge, which is consistent with previous observations (Williams 1989;Pawar and Kamra 2004;Qie et al 2005;Nag and Rakov 2009). However, Case 4 shows a stronger net positive charge region than Case 2, contributing to the initiation of more -CG flashes.…”

Anomalous electric field changes and high flash rate beneath a thunderstorm in northeast India

“…It is worthy to note that both these electric field changes are of equal magnitude. Pawar and Kamra (2004) have already reported such two-polarity electric field changes, one followed immediately by another. They have attributed this to two different lightning discharges of opposite polarity.…”

Effects of environmental conditions on inducing charge structures of thunderstorms over Eastern India

“…Electrical structure of the thunderstorm Previous studies have revealed that in thunderstorms with non-inverted polarity charge structures (with midlevel negative and upper level positive charge regions), most of the electric field changes produced by lightning are of negative polarity, indicating removal of negative charge from overhead (Jacobson and Krider 1976;Livingston and Krider 1978;Mohanty and Pradeep Kumar 2004;Pawar and Kamra 2004 (Figures 4 and 5). Although it is difficult to distinguish the CG from the IC discharges based only on singlepoint observations of the electric field and Maxwell current data, most of the visually confirmed CG discharges were found to be transporting positive charge to the ground on May 11.…”

“…Furthermore, the median negative peak current in severe storms was very low (i.e., as low as 12 to 16 kA) and was noticeably less than in nonsevere storms (i.e., by at least 10%). Although earlier reports suggest most thunderstorms with inverted polarity charge structures were characterized by a high degree of severity, Qie et al (2005) and Kamra (2004 and2009) have also reported some non-severe thunderstorms over the Tibetan Plateau and India, with a wide spread and strong positive charge in the lower portion of cloud. Majority of lightning activity arises from lower negative dipole of these thunderclouds.…”