Lightning

About: Lightning is a research topic. Over the lifetime, 15150 publications have been published within this topic receiving 180556 citations.

NOx from lightning 1. Global distribution based on lightning physics

Abstract: This paper begins a study on the role of lightning in maintaining the global distribution of nitrogen oxides (NOx) in the troposphere. It presents the first global and seasonal distributions of lightning-produced NOx (LNOx) based on the observed distribution of electrical storms and the physical properties of lightning strokes. We derive a global rate for cloud-to-ground (CG) flashes of 20–30 flashes/s with a mean energy per flash of 6.7×109 J. Intracloud (IC) flashes are more frequent, 50–70 flashes/s but have 10% of the energy of CG strokes and, consequently, produce significantly less NOx. It appears to us that the majority of previous studies have mistakenly assumed that all lightning flashes produce the same amount of NOx, thus overestimating the NOx production by a factor of 3. On the other hand, we feel these same studies have underestimated the energy released in CG flashes, resulting in two negating assumptions. For CG energies we adopt a production rate of 10×1016 molecules NO/J based on the current literature. Using a method to simulate global lightning frequencies from satellite-observed cloud data, we have calculated the LNOx on various spatial (regional, zonal, meridional, and global) and temporal scales (daily, monthly, seasonal, and interannual). Regionally, the production of LNOx is concentrated over tropical continental regions, predominantly in the summer hemisphere. The annual mean production rate is calculated to be 12.2 Tg N/yr, and we believe it extremely unlikely that this number is less than 5 or more than 20 Tg N/yr. Although most of LNOx, is produced in the lowest 5 km by CG lightning, convective mixing in the thunderstorms is likely to deposit large amounts of NOx, in the upper troposphere where it is important in ozone production. On an annual basis, 64% of the LNOx, is produced in the northern hemisphere, implying that the northern hemisphere should have natural ozone levels as much as 2 times greater than the southern hemisphere, even before anthropogenic influences. The amount of O3 produced from this NOx is expected to exceed the stratospheric source by a factor of 1.5, and thus the hemispheric asymmetry in LNOx would lead to a significant excess of northern hemisphere O3 even in the preindustrial troposphere. (The monthly climatologies for LNOx on a 1°×1° latitude-longitude grid can be obtained by e-mail to cprice@flash.tau.ac.il).

Television image of a large upward electrical discharge above a thunderstorm system.

Abstract: An image of an unusual luminous electrical discharge over a thunderstorm 250 kilometers from the observing site has been obtained with a low-light-level television camera. The discharge began at the cloud tops at 14 kilometers and extended into the clear air 20 kilometers higher. The image, which had a duration of less than 30 milliseconds,resembled two jets or fountains and was probably caused by two localizd electric charge concentrations at the cloud tops. Large upward discharges may create a hazard for aircraft and rocket launches and, by penetrating into the ionosphere, may initiate whistler waves and other effects on a magnetospheric scale. Such upward electrical discharges may account for unexplained photometric observations of distant lightning events that showed a low rise rate of the luminous pulse and no electromagnetic sferic pulse of the type that accompanies cloud-to-earth lightning strokes. An unusually high rate of such photometric events was recorded during the night of 22 to 23 September 1989 during a storm associated with hurricane Hugo.

Magnetic field of lightning return stroke

Abstract: The magnetic flux density due to first and to subsequent lightning return strokes is calculated for distances from the strokes of 0.5 to 200 km. The basis of the calculations is various assumed forms for the channel current as a function of time and of channel height. Two new channel-current models are introduced for first strokes and one new model for subsequent strokes, in addition to the use of the models of Bruce and Golde and of Dennis and Pierce. The new models provide a better approximation to the real lightning channel current than do the previous models, but all models considered yield radiation fields far from the channel that are consistent with experiment. It is shown that, contrary to the claims of Norinder and co-workers, the magnetic-field rise time for a stroke within a distance of about 20 km is essentially unrelated to the current rise time in the stroke channel base. For subsequent strokes, field rise times of many tens of microseconds can be due to current rise times shorter than a microsecond. On the other hand, field rise times for subsequent strokes may be strongly influenced by current fall times. The analysis of Norinder and co-workers which relates peak channelbase current to peak magnetic field yields values of current that can be considered accurate to about a factor of 2.

Influence of a lossy ground on lightning-induced voltages on overhead lines

Abstract: A comprehensive study on the effect of a lossy ground on the induced voltages on overhead power lines by a nearby lightning strike is presented The ground conductivity plays a role in both the evaluation of the lightning radiated fields and of the line parameters To be calculated by means of a rigorous theory, both fields and line constants need important computation time, which, for the problem of interest, is still prohibitive The aim of this paper is to discuss and analyze the various simplified approaches and techniques that have been proposed for the calculation of the fields and the line constants when the ground cannot be assumed as a perfectly conducting plane Regarding the radiated electromagnetic field, it is shown that the horizontal electric field, the component which is most affected by the ground finite conductivity, can be calculated in an accurate way using the Cooray-Rubinstein simplified formula The presence of an imperfectly conducting ground is included in the coupling equations by means of two additional terms: the longitudinal ground impedance and the transverse ground admittance, which are both frequency-dependent The latter can generally be neglected for typical overhead lines, due to its small contribution to the overall transverse admittance of the line Regarding the ground impedance, a comparison between several simplified expressions used in the literature is presented and the validity limits of these expressions are established It is also shown that for typical overhead lines the wire impedance can be neglected as regard to the ground impedance