Upward lightning observations from towers in Rapid City, South Dakota and comparison with National Lightning Detection Network data, 2004-2010 (original) (raw)
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Upward Lightning Triggering Study ( UPLIGHTS ) : Project Summary and Initial Findings
2018
The Upward Lightning Triggering Study (UPLIGHTS) took place in Rapid City, South Dakota, USA from 2012 through 2014. 38 upward flashes were observed during the summer thunderstorm months (Apr – Sep) with a combination of highand standard-speed video and digital still cameras, electric field meters, fast antenna systems, and for the 2014 season, a Lightning Mapping Array. All upward flashes were triggered by preceding lightning activity with the +CG flash the dominate triggering type. Intracloud and post +CG return stroke negative leaders passing near the towers were the primary triggering flash component, 2.4 times more frequent than the +CG return stroke triggering component. The one observed upward negative leader was triggered by a preceding -CG return stroke. Keywords—upward lightning, triggering, initiation
On the Triggering Mechanisms of Upward Lightning
Scientific Reports, 2019
Upward lightning studies took place in Rapid City, South Dakota, USA and S. Paulo, Brazil during the summer thunderstorm seasons from 2011 to 2016. One of the main objectives of these campaigns was to evaluate and characterize the triggering of upward positive leaders from tall objects due to preceding nearby flash activity. 110 upward flashes were observed with a combination of high- and standard-speed video and digital still cameras, electric field meters, fast electric-field antenna systems, and for two seasons, a Lightning Mapping Array. These data were analyzed, along with correlated lightning location system data, to determine the triggering flash type responsible for the initiation of upward leaders from towers. In this paper, we describe the various processes during flash activity that can trigger upward leaders from tall objects in the USA and in Brazil. We conclude that the most effective triggering component is the propagation of the in-cloud negative leader during the co...
Journal of Geophysical Research, 1991
The frequency distribution of the peak signal strength associated with the first detected return stroke of positive and negative cloud-to-ground flashes was studied using lightning data from northeastern Colorado. These data were obtained during 1985 with a network of medium-high gain direction finders (DFs) having a nominal range of 300 km. The median normalized signal strength of positive flashes was almost 2 times that of the negatives for flashes within 300 km of the DFs (170 versus 96 Lightning Location and Protection, Inc. (LLP), units). These DFs have an inherent detection threshold bias that tends to discriminate against weak signals. This bias increases with range and affects the detection of positive and negative flashes in different ways because of the differing character of their distributions. Positive flashes appear to have a large percentage (12 times larger than that of negative flashes) of signals clustered around very weak values (below 30 units) that are lost to the Colorado detection system of medium-high gain very quickly with increasing range (most of these are undetected by 125 km). The resulting median for positive signals thus could appear to be much larger than the median for negative signals, which are more clustered around intermediate values (80 units). When only flashes very close (20-60 km) to the DFs are considered, however, the two distributions have almost identical medians (70 units). The large percentage of weak positive signals (below 30 units) detected close to the DFs (about 10 times larger than that of negative signals) has not been previously explored. It has been suggested that they come from intracloud discharges and are improperly classified as coming from CG flashes. The evidence in hand, however, points to their being real positive, albeit weak, cloud-toground flashes. Whether or not they are real positive ground flashes, it is important to be aware of their presence in data from magnetic DF networks. Even if the weak positive signals are eliminated by considering only distant flashes (beyond about 125 km), the frequency distributions of positive and negative signal strengths are very different, the positives lacking the large percentage of intermediate signals (around 80 units) of the negatives but having a somewhat larger relative frequency of large and very large signals (beyond 130 units). 22,307 22,308 L6PEZ ET AL.: SIGNAL STRENGTH OF CLOUD-TO-GROUND LIGHTNING ß . ß ß ß ß " Negative (82,059) ß .; ß ß Negative (26,834) ., ß ., ß ß ß ß ß ß ....'" Positive ß (659) ß © ß e e e e ß e ß e eeeeeeee __ e e e e ß ... •e•ative$ _ ß ß e ß ©ee e e e ß ee ß -ß eeeee ee ß ß e ee ß ß e
Correlated observations of three triggered lightning flashes
Journal of Geophysical Research, 1984
International Program (TRIP '81) at Langmuir Laboratory, New Mexico, has resulted in the determination of three-dimensional return stroke propagation speeds and peak currents for 56 subsequent strokes. We find a nonlinear relationship between the return stroke propagation speed and the stroke peak current that is qualitatively similar to that proposed by both Lundholm and Wagner. A nonlinear correlation is also found between the return stroke propagation speed and the dart leader propagation speed for 32 strokes. Linear correlation coefficients are evaluated for the following quantities' dart leader propagation speed and ensuing return stroke peak current (32 strokes; r = 0.84); stroke peak current and interstroke interval (69 strokes; r = 0.57); return stroke propagation speed and interstroke interval (56 strokes' r = 0.49); dart leader propagation speed and interstroke interval (32 strokes; r = 0.43). The wea_k positive correlation found between the dart leader propagation speed and the interstroke interval contradicts previous corresponding natural lightning observations. The mean three-dimensional return stroke propagation speed for 56 strokes is 12 x 10 ? m/s with a range of 6.7 x 10 ? m/s to 17 x 10 ? m/s; the mean three-dimensional propagation speed found for 32 dart leaders is 20 x 10 6 m/s with a range of 9.5 X 10 6 m/s to 43 x 10 6 m/s. The mean dart length measured is 50 m with a range of 15-90 m. In two of the three flashes, the downward propagating dart leaders appear to meet upward propagating streamers at heights of approximately 20 and 30 m, respectively. TRIGGERED LIGHTNING RETURN STROKES TRIP•BI; oeG STROKES ß ß ß ß ee e ee ß ß ß g --B.q..q I oe I NTERSTRnKE INTERVRL (,MS) Return stroke propagation speed versus interstroke interval.
Cloud-to-ground lightning flash characteristics in the contiguous United States: 1989–1991
Journal of Geophysical Research, 1994
Wideband magnetic direction finders have been used to obtain a cloud-to-gro_und lightning flash count for the contiguous United States, an area of 7.7 x 10 6 km 2, for the period 1989 through 1991. Over 46 million flashes to ground were recorded and are divided among the three years, 13.4 million in 1989, 15.9 million in 1990, and 16.9 million in 1991. Maximum flash densities occur in Florida and increase each year, from 9 flashes km -2 (1989) to 13 flashes km -2 (1991). The database contains 1.7 million positive flashes divided among the three years, 0.4 million in 1989, 0.6 million in 1990, and 0.7 million in 1991. In 1990 and 1991 the positive flash density maximum occurred in Florida but elsewhere in 1989. Secondary maximum positive flash densities occur throughout the Midwest. The annual mean percentage of positive flashes in the total lightning count is 3.7% for the period 1989-1991. The interannual variation is small, ranging from 3.1% (1989) to 4.0% (1991). However, in any given year the geographical variation of the percentage of positive flashes is large. The percentage of positive flashes is 2% (1989) at the latitude of Florida but near 25% and higher at the latitudes of the upper Midwest, Maine, and Oregon.
Upward lightning flashes characteristics from high‐speed videos
Journal of Geophysical Research: Atmospheres, 2016
One hundred high‐speed video recordings (72 cases in Brazil and 28 cases in USA) of negative upward lightning flashes were analyzed. All upward flashes were triggered by another discharge, most of them positive CG flashes. A negative leader passing over the tower(s) was frequently seen in the high‐speed video recordings before the initiation of the upward leader. One triggering component can sometimes initiate upward leader in several towers. Characteristics of leader branching, ICC pulses, recoil leader incidence, and interpulse interval are presented in this work. A comparison of the results is done for data obtained in Brazil and USA. The duration of ICC and the total flash duration are on average longer in Brazil than in USA. Only one fourth of all upward leaders are followed by any return strokes both in Brazil and USA, and the average number of return strokes following each upward leader is very low. The presence and duration of CC following return strokes in Brazil is more th...
Parameters of triggered-lightning flashes in Florida and Alabama
Journal of Geophysical Research, 1993
Channel base currents from triggered lightning were measured at the NASA Kennedy Space Center, Florida, during summer 1990 and at Fort McClellan, Alabama, during summer 1991. Additionally, 16-mm cinematic records with 3-or 5-ms resolution were obtained for all flashes, and streak camera records were obtained for three of the Florida flashes. The 17 flashes analyzed here contained 69 strokes, all lowering negative charge from cloud to ground. Statistics on interstroke interval, no-current interstroke interval, total stroke duration, total stroke charge, total stroke action integral ($ i 2dt), return stroke current wave front characteristics, time to half peak value, and return stroke peak current are presented. Return stroke current pulses, characterized by rise times of the order of a few microseconds or less and peak values in the range of 4 to 38 kA, were found not to occur until after any preceding current at the bottom of the lightning channel fell below the noise level of less than 2 A. Current pulses associated with M components, characterized by slower rise times (typically tens to hundreds of microseconds) and peak values generally smaller than those of the return stroke pulses, occurred during established channel current flow of some tens to some hundreds of amperes. A relatively strong positive correlation was found between return stroke current average rate of rise and current peak. There was essentially no correlation between return stroke current peak and 10-90% rise time or between return stroke peak and the width of the current waveform at half of its peak value.
Bipolar cloud‐to‐ground lightning flash observations
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...