Automatic Studies of Continuing Current in Lightning Flashes

Journal of Geophysical Research, 2010

Bulletin of the American Meteorological Society, 2016

A World Meteorological Organization weather and climate extremes committee has judged that the world’s longest reported distance for a single lightning flash occurred with a horizontal distance of 321 km (199.5 mi) over Oklahoma in 2007, while the world’s longest reported duration for a single lightning flash is an event that lasted continuously for 7.74 s over southern France in 2012. In addition, the committee has unanimously recommended amendment of the AMS Glossary of Meteorology definition of lightning discharge as a “series of electrical processes taking place within 1 s” by removing the phrase “within 1 s” and replacing it with “continuously.” Validation of these new world extremes 1) demonstrates the recent and ongoing dramatic augmentations and improvements to regional lightning detection and measurement networks, 2) provides reinforcement regarding the dangers of lightning, and 3) provides new information for lightning engineering concerns.

2009

Lightning is a natural but destructive phenomenon that affects various locations on the earth’s surface every year. Uman (1968) defines lightning as a selfpropagating atmospheric electrical discharge that results from the accumulation of positive and negative space charge, typically occurring within convective clouds. This electrical discharge can occur in two basic ways: cloud flashes and ground flashes (MacGorman and Rust 1998, p. 83). The latter affects human activity, property and life. Curran et al. (2000) find that lightning is ranked second behind flash and river flooding as causing the most deaths from any weather-related event in the United States. From 1959 to 1994, there was an average of 87 deaths per year from lightning. Curran et al. also rank the state of Texas as third in the number of fatalities from 1959 to 1994, behind Florida at number one and North Carolina at number two. There is an obvious need for the protection of life and property from lightning flashes to ...

Journal of Geophysical Research: Atmospheres, 2020

Downward Terrestrial Gamma-ray Flashes occur during strong initial breakdown pulses of negative cloud-to-ground and cloud lightning. • The initial breakdown pulses consist of streamer-based fast negative breakdown having transient sub-pulse conducting events, or 'sparks'. • The streamer to leader transition of negative stepping occurs during strong currents in the final stage of initial breakdown pulses.

Journal of Geophysical Research: Atmospheres, 2013

Bipolar lightning is usually defined as a lightning flash where the current waveform exhibits a polarity reversal. There are very few reported cases of cloud‐to‐ground (CG) bipolar flashes using only one channel in the literature. Reports on this type of bipolar flashes are not common due to the fact that in order to confirm that currents of both polarities follow the same channel to the ground, one necessarily needs video records. This study presents five clear observations of single‐channel bipolar CG flashes. High‐speed video and electric field measurement observations are used and analyzed. Based on the video images obtained and based on previous observations of positive CG flashes with high‐speed cameras, we suggest that positive leader branches which do not participate in the initial return stroke of a positive cloud‐to‐ground flash later generate recoil leaders whose negative ends, upon reaching the branch point, traverse the return stroke channel path to the ground resulting...

Journal of Geophysical Research, 2010

Although positive lightning flashes to ground are not as frequent as negative flashes, their large amplitudes and destructive characteristics make understanding their parameters an important issue. This study summarizes the characteristics of 103 positive cloud-to-ground (+CG) flashes that have been recorded using high-speed video cameras (up to 11,800 frames per second) in three countries together with time-correlated data provided by

Geophysical Research Letters, 2016

An X-band polarimetric radar and multiple lightning detection systems are used to document the initial cloud-to-ground lightning flash in a large number (46 cases) of incipient thunderstorms, as part of the CHUVA-Vale field campaign during the 2011/2012 spring-summer in southeast Brazil. The results show an exceptionally low stroke multiplicity (87% of flashes with single stroke) in the initial ground flashes, a finding consistent with the limited space available for the positive leader extension into new regions of negative space charge in compact cells. The results here are contrasted with the behavior of ground flashes in mesoscale thunderstorms in previous studies. Additionally, we found evidence for a minimum scale (radar echo >20 dBZ) for lightning initiation (>3 km in radius) and that the peak currents of initial cloud-to-ground flashes in these compact thunderstorms are only half as large as return stroke peak currents in general.

Journal of Applied Meteorology and Climatology, 2015

Changes in lightning characteristics over the conterminous United States (CONUS) are examined to support the National Climate Assessment (NCA) program. Details of the variability of cloud-to-ground (CG) lightning characteristics over the decade 2003-12 are provided using data from the National Lightning Detection Network (NLDN). Changes in total (CG 1 cloud flash) lightning across part of the CONUS during the decade are provided using satellite Lightning Imaging Sensor (LIS) data. The variations in NLDN-derived CG lightning are compared with available statistics on lightning-caused impacts to various U.S. economic sectors. Overall, a downward trend in total CG lightning count is found for the decadal period; the 5-yr mean NLDN CG count decreased by 12.8% from 25 204 345.8 (2003-07) to 21 986 578.8 (2008-12). There is a slow upward trend in the fraction and number of positive-polarity CG lightning, however. Associated lightning-caused fatalities and injuries, and the number of lightning-caused wildland fires and burn acreage also trended downward, but crop and personal-property damage costs increased. The 5-yr mean LIS total lightning changed little over the decadal period. Whereas the CONUSaveraged dry-bulb temperature trended upward during the analysis period, the CONUS-averaged wet-bulb temperature (a variable that is better correlated with lightning activity) trended downward. A simple linear model shows that climate-induced changes in CG lightning frequency would likely have a substantial and direct impact on humankind (e.g., a long-term upward trend of 18C in wet-bulb temperature corresponds to approximately 14 fatalities and over $367 million in personal-property damage resulting from lightning).

This study revisits the sprite polarity paradox, first manifest by observations that exceptional cloud-to-ground flashes with negative polarity generally did not produce detectable sprites. The paradox is here resolved by the Transient Luminous Event (TLE) known as the halo, which on account of its inferior brightness (0.3 MR versus 1.5 MR) and substantially shorter duration (1 ms versus 10-100 ms) in comparison with the sprite, is not readily detectable in ground-based video cameras with standard field duration (16.7-20 ms). Observations with improved temporal resolution (ISUAL (Imager of Sprites and Upper Atmospheric Lightnings) from space and PIPER (Photometric Imager of Precipitated Electron Radiation) observations from the ground) provide evidence that flashes with negative polarity dominate the global halo population, and that the halo numbers are more than sufficient to account for the previously missing TLEs. The evidence for lightning polarity-dependent TLEs (sprites, positive and halos, negative) is attributable to the well established but incompletely understood contrast in the behavior of negative and positive lightning flashes to ground.

Monthly Weather Review, 2013

In measurements of the electric field associated with the current of a sprite 450 km from ground-based field sensors, it was observed that the sign of the electric field was positive when positive charge was lowered from the ionosphere. A recent model for the electric field associated with the sprite current also predicts positive field changes at 450 km from the sprite. A well-known analysis of a vertical dipole in a thundercloud shows that the electric field on the ground reverses its sign at an easily computed distance from the dipole. A similar simplified electrostatic analysis of a sprite predicts a field reversal distance around 130 km. A more accurate electrodynamic analysis based on Maxwell’s equations indicates that the field reversal distance should be between 70 and 80 km.