Within the Charlotte, North Carolina, to Atlanta, Georgia, megaregion (Charlanta), the Atlanta metropolitan area has been shown to augment proximal cloud‐to‐ground (CG) lightning occurrence. Although ...numerous studies have documented this “urban lightning effect” (ULE) with regard to CG lightning, relatively few have investigated urban effects on distributions of total lightning (TL). Moreover, there has yet to be a study of the ULE using TL observations from the Geostationary Lightning Mapper (GLM). In an effort to fill this gap, we investigated spatial distributions of TL around the cities of Atlanta, GA, Greenville, SC, and Charlotte, NC, using GLM data collected during the warm seasons of 2018–2021. Analyses reveal augmentation of TL intensity and frequency over the major cities of Atlanta and Charlotte, with a diminished urban signal over the smaller city of Greenville. This work also demonstrated the potential efficacy of the emerging satellite‐based TL climatology in ULE studies.
Plain Language Summary
Studies using ground‐based lightning detection networks have revealed an “urban lightning effect” (ULE) around major cities. In 2016, the U.S. launched a weather satellite with a unique lightning mapping instrument. This study, possibly for the first time, demonstrated the ability to utilize space‐based observation of total lightning to detect the ULE within the Charlotte, North Carolina, to Atlanta, Georgia, urban corridor. The study also paves the way for future ULE analyses as the satellite lightning data record lengthens.
Key Points
The urban lightning effect (ULE) is detectable in Geostationary Lightning Mapper total lightning observations
The ULE is most discernible in the larger metropolitan areas of the Charlotte, NC, to Atlanta, GA, urban corridor
The emerging Geostationary Lightning Mapper data set enables a new generation of urban lightning studies as the record lengthens
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We report on upward lightning observations from ten tall towers (91–191 m) in Rapid City, South Dakota, USA and compare with National Lightning Detection Network (NLDN) data. A total of 81 upward ...flashes were observed from 2004–2010 using GPS time‐stamped optical sensors, and in all but one case, visible flash activity preceded the development of the upward leaders. Time‐correlated analysis showed that the NLDN recorded an event within 50 km of towers and within 500 ms prior to upward leader development from the tower(s) for 83% (67/81) of the upward flashes. A preceding positive cloud‐to‐ground stroke (+CG) was detected in 57% (46/81) of the cases, and a preceding positive intracloud flash (+IC) in 23% (19/81) of the cases. However, 8 of the 19 NLDN‐indicated +IC events were actually +CG strokes based on optical observations. Preceding negative intracloud flashes (−IC) were recorded for 2% (2/81) of the cases. Analysis also showed that for 44% (36/81) of the upward flashes, the NLDN reported subsequent negative cloud‐to‐ground (−CG) strokes and/or −IC events at one or more tower locations. Of the 151 subsequent events, 70% (105/151) were −CG reports and 30% (46/151) were listed as −IC events. The geometric mean/median location accuracy and peak current for subsequent events were 194 m/206 m and −12.9 kA/−12.4 kA respectively. These correlated observations suggest that a majority of the upward lightning flashes were triggered by a preceding flash with the dominant triggering type being the +CG flash.
Key Points
Summer season upward positive leaders triggered by nearby +CG flashes
Impulsive connections by recoil leaders that form on cutoff upward branches
Less than half upward positive leaders produced NLDN‐indicated impulsive events
Cloud-to-ground (CG) lightning data from the European Cooperation for Lightning Detection (EUCLID) network over the period 2006–2014 are explored. Mean CG flash densities vary over the European ...continent, with the highest density of about 6 km−2 yr−1 found at the intersection of the borders between Austria, Italy and Slovenia. The majority of lightning activity takes place between May and September, accounting for 85 % of the total observed CG activity. Furthermore, the thunderstorm season reaches its highest activity in July, while the diurnal cycle peaks around 15:00 UTC. A difference between CG flashes over land and sea becomes apparent when looking at the peak current estimates. It is found that flashes with higher peak currents occur in greater proportion over sea than over land.
The effects of generating pulsed radiation by a long spark discharge are important for the development of lightning models and applications related to lightning protection. In experiments with a Marx ...generator simulating a lightning discharge, we detected the radiation in the form of a single ultrawideband electromagnetic pulse (UWB EMP) about 200 ps in duration, and rising time about 100 ps. UWB EMP generation occurs during the breakdown of a “rod–rod” 4 m long gap. Pulses of almost unipolar shape are observed in more than half of all positive discharges. EMP emission occurs before the main stage, and corresponds to the start of the upward leader from a grounded electrode. In negative discharges, pulses are also observed, but less frequently and with a smaller amplitude. The UWB EMPs, given their large amplitude (more than 100 V/m at a distance of 90 m from the discharge), can be considered as possible new lightning damage factors.
Plain Language Summary
A Marx generator with an operating voltage of several megavolts is used to simulate a lightning stroke of a grounded object. The generation of a short electromagnetic pulse (several hundreds of picoseconds long) has been detected during a breakdown of a long air gap using special electromagnetic probes. Such a pulse is observed in the majority of positive discharges in the “rod–rod” gap. Subnanosecond pulse can be regarded as possible new damage factor of lightning strokes.
Key Points
Marx generator allows studying generation of ultra‐wideband electromagnetic pulses (EMPs) by long spark discharges that model lightning
Single EMP about 200 ps duration is generated by 4‐m long spark discharge in a rod‐rod geometry
Pulses of almost unipolar shape with up to 200 V/m amplitude are observed at 90 m distance from more than half of all positive discharges
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Wind turbines (WTs) can beseriously damaged by lightning strikes and they can be struck by a significant number of flashes. This should be taken into account when the WT lightning protection system ...is designed. Moreover, WTs represent a path for the lightning current that can modify the well-known effects of the lightning discharge in terms of radiated electromagnetic fields, which are a source of damage and interference for nearby structures and systems. In this paper, a WT struck by a lightning discharge is analyzed with a full-wave modelling approach, taking into account the details of the WT and its interactions with the lightning channel. The effects of first and subsequent return strokes are analyzed as well as that of the rotation angle of the struck blade. Results show that the lightning current along the WT is mainly affected by the ground reflection and by the reflection between the struck blade and the channel. The computed electromagnetic fields show that, for subsequent return strokes, the presence of a WT almost doubles their magnitude with respect to a lightning striking the ground. Such enhancement is emphasized when the inclined struck blade is considered.
Abstract
The duration and horizontal extension distance (HED) of intracloud (IC), negative cloud‐to‐ground (NCG), positive cloud‐to‐ground (PCG), and bipolar cloud‐to‐ground (BCG) lightning are ...analyzed using data from the Oklahoma Lightning Mapping Array and the National Lightning Detection Network. All of these conform to lognormal distributions. BCG lightning has the greatest average spatiotemporal size, owing to its longest‐duration and largest‐spatial‐extension discharge process after the first return stroke (RS). Compared with NCG lightning, PCG lightning tends to include longer‐duration and greater‐spatial‐extension discharge processes before the first RS, making the latter have a larger average spatiotemporal size. IC lightning exhibits the smallest average spatiotemporal size, with a higher concentration of samples in smaller size intervals. Overall, as lightning initiation heights increase, IC and NCG lightning duration tends to increase, while NCG lightning variation is mainly due to discharge processes before the first RS. HED of both types initially increases and then decreases, peaking at ∼7 km. The horizontal extension speed (HES) of IC lightning tends to decrease with increasing initiation height, while for NCG lightning, the HES associated with discharge processes before the first RS shows a clearer decreasing trend at higher levels. The NCG lightning initiated below ∼6 km tends to exhibit similar HED before the first RS and increased HED after the first RS. However, for NCG lightning initiated above ∼6 km, the HED before the first RS is notably greater than the increased HED after the first RS.
Plain Language Summary
This study examines the duration of discharge processes and horizontal extension distance (HED) of intracloud (IC) lightning, which propagates only within or between clouds, and cloud‐to‐ground (CG) lightning, including positive cloud‐to‐ground (PCG), negative cloud‐to‐ground (NCG), and bipolar cloud‐to‐ground (BCG) lightning, which transfers positive, negative, and both positive and negative charges to the earth via one or more grounded channels, respectively. On average, BCG lightning exhibits the largest spatiotemporal size, followed by PCG, NCG, and IC lightning. CG lightning is divided into two stages: discharge processes before and after the first return stroke (RS), an intense neutralization process when the channel first connects the cloud and earth. In the first stage, PCG lightning typically exhibits a greater spatiotemporal size than NCG lightning. In the second stage, BCG lightning has a significantly larger spatiotemporal size than both PCG and NCG lightning. Higher‐initiated IC and NCG lightning tend to have a longer duration and smaller horizontal extension speed than lower‐initiated lightning. IC and NCG lightning both tend to have larger HED at middle levels. For NCG lightning initiated above ∼6 km, the discharge process before the first RS contributes more to the HED.
Key Points
The study uncovers how the spatiotemporal sizes of intracloud (IC) and negative cloud‐to‐ground (NCG) lightning flashes change as the lightning initiation height increases
Bipolar cloud‐to‐ground (BCG) lightning has the largest spatiotemporal size on average, followed by positive cloud‐to‐ground (PCG), NCG, and IC lightning in that order
Larger sizes of PCG and BCG lightning primarily benefit from the discharge processes before and after the first return stroke, respectively
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