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New results of lightning observations, in Planetary Electrodynamics. Proceedings of the 4th International Conference on the Universal Aspects of Atmospheric Electricity
... m were also estimated. The former is significantly smaller than typically observed downward leader lengths of the order of several kilometers, while the latter is consistent with previous studies [Berger and Vogelsanger, 1969] on upward initiated negative stepped leaders. [33] Acknowledgments. ...
We report the measured current characteristics of positive lightning
discharges to the Gaisberg Tower (GBT) in Austria from 2000 to 2009. On
the basis of the recorded current waveforms, a total of 26 flashes
consisting of initial stage only were identified as upward positive
discharges initiated by an upward negative leader from GBT. They
accounted for 4% (26/652) of the total flashes recorded at the GBT.
Nineteen (73%) out of the 26 positive flashes occurred during
nonconvective season (September-March). Median values of flash peak
current, flash duration, charge transfer, and action integral were
determined as 5.2 kA, 82 ms, 58 C, and 0.16 × 103
A2 s, respectively. Current pulses of high repetition rate
superimposed on the initial portion of initial continuous current are
inferred to be associated with the upward negative stepped leader
process. The weighted arithmetic means of leader pulse peak current,
leader pulse duration, leader interpulse interval, and leader pulse
charge are 3 kA, 31 μs, 32 μs, and 42 mC, respectively. On the
basis of an assumed stepped leader speed in the range of 8 ×
104 to 4.5 × 105 m/s an upward negative
stepped leader channel charge density of 15-87 mC/m, a leader length of
168-945 m, and an average leader step length of 2.4-13.3 m were
estimated. The upward negative stepped leader channel charge density and
length are significantly larger and smaller than their counterparts in
downward negative stepped leaders, respectively, while the upward leader
step length is consistent with previous studies. Possible reasons for
this are discussed.
... He also obtained time-resolved photographic images of upward lightning. Berger and co-workers acquired detailed current and optical data for upward lightning in their longterm study at the Mount San Salvatore in Switzerland [e.g., Berger and Vogelsanger, 1969]. Similar studies, mostly at instrumented towers, were conducted in several other countries, including Austria, Canada, Germany, Japan, and Russia (see Rakov and Uman [2003, chap. ...
We analyzed high-speed video images and corresponding current records for eight upward lightning flashes initiated by the Peissenberg tower (160 m) in Germany. These flashes contained a total of 33 measurable initial stage (IS) current pulses, which are superimposed on steady IS currents. Seven IS pulses had relatively short (8 mus) risetimes. Six (86%) of seven IS current pulses with shorter risetimes each developed in a newly-illuminated branch, and 25 (96%) of 26 IS pulses with longer risetimes occurred in already luminous (current-carrying) channels. These results support the hypothesis that longer risetimes are indicative of the M-component mode of charge transfer to ground, while shorter risetimes are associated with the leader/return stroke mode. Similar results were obtained for M-component pulses that are superimposed on continuing currents following return-stroke pulses.
Spatial analyses of cloud-to-ground (CG) lightning occurrence due to a rapid expansion in the number of antenna towers across the United States are explored by gridding 20 years of National Lightning Detection Network data at 500 m spatial resolution. The 99.8% of grid cells with ≥100 CGs were within 1 km of an antenna tower registered with the Federal Communications Commission. Tower height is positively correlated with CG occurrence; towers taller than 400 m above ground level experience a median increase of 150% in CG lightning density compared to a region 2 km to 5 km away. In the northern Great Plains, the cumulative CG lightning density near the tower was around 138% (117%) higher than a region 2 to 5 km away in the September–February (March–August) months. Higher CG frequencies typically also occur in the first full year following new tower construction, creating new lightning hot spots.
The upward lightning (UL) initiated from the top of tall buildings (at least above 100 m) is a type of atmospheric discharge. Currently, we understand the nature of the UL from ground observations, but the corresponding theoretical research is lacking. Based on an existing bidirectional leader stochastic model, a stochastic parameterization scheme for the UL has been built and embedded in an existing two-dimensional thundercloud charge/discharge model. The ULs simulated from the experiments with two-dimensional high resolution agree generally with the observation results. By analyzing the charge structure of thunderstorm clouds, we determined the in-cloud environmental characteristics that favor the initiation of conventional cloud-to-ground (CG) flashes and analyzed the differences and similarities of some characteristics of the positive and the negative UL. Simulation results indicate that the positive ULs are typically other-lightning-triggered ULs (OLTUL) and are usually a discharge phenomenon between the ground and the lower positive charge region appearing below the main middle negative charge region. The effect of the previous in-cloud lightning (IC) process of space electrical field provides favorable conditions for the initiation of a positive UL. Its entire discharge process is limited, and the branches of the leader are fewer in number as its discharge is not sufficient. A negative UL is generally a discharge phenomenon of the dipole charge structure between the ground and the main negative charge region. The lower temperature stratification and the sinking of the hydrometeors typically initiate a negative UL. Negative ULs develop strongly and have more branches. The OLTUL is initiated mainly during the development stage of a thunderstorm, while the self-triggered UL (STUL) is initiated mainly during the dissipation stage of a thunderstorm.
[1] A color photograph has been obtained of a negative lightning leader in clear air at 10.3 km altitude. The individual leader steps are resolved as relatively straight segments of at least ∼200 m in length, between sharp kinks (nodes) in the channel. Each node is accompanied by a group of streamers of ∼100 m in length. One node has an unconnected secondary leader with streamers at both ends. Lightning Mapping Array observations show that the leader was part of an intracloud (IC) flash.The observation shows that steps of negative leaders near 10 km altitude are an order of magnitude longer than values reported in the literature for negative leaders near sea level. Since negative leaders propagate at comparable velocities at low and high altitudes, stepping occurs at a lower rate in IC flashes, which can explain why RF emissions from IC flashes are more intermittent than those from cloud-to-ground flashes.
Despite being one of the most familiar and widely recognized natural phenomena, lightning remains relatively poorly understood. Even the most basic questions of how lightning is initiated inside thunderclouds and how it then propagates for many tens of kilometers have only begun to be addressed. In the past, progress was hampered by the unpredictable and transient nature of lightning and the difficulties in making direct measurements inside thunderstorms, but advances in instrumentation, remote sensing methods, and rocket-triggered lightning experiments are now providing new insights into the physics of lightning. Furthermore, the recent discoveries of intense bursts of X-rays and gamma-rays associated with thunderstorms and lightning illustrate that new and interesting physics is still being discovered in our atmosphere. The study of lightning and related phenomena involves the synthesis of many branches of physics, from atmospheric physics to plasma physics to quantum electrodynamics, and provides a plethora of challenging unsolved problems. In this review, we provide an introduction to the physics of lightning with the goal of providing interested researchers a useful resource for starting work in this fascinating field.
We examine in detail the simultaneous lightning current waveforms, close
electric field changes, and lightning location system data for upward
lightning discharges initiated from the Gaisberg Tower (GBT) from 2005
to 2009. Out of 205 upward flashes, most of them (87% or 179/205) were
initiated from the tower top without any nearby preceding lightning
activity (called "self-initiated"), whereas 26 upward flashes (13%) were
initiated from the tower top with immediately preceding nearby lightning
activity (called "nearby-lightning-triggered"), including 15 positive
ground flashes, one negative ground flashes, and 10 cloud discharges.
The possible reasons for self-initiated upward flashes dominating at the
GBT could be the field enhancement due to the Gaisberg Mountain above
the surrounding terrain and low altitude of charge region during
non-convective season (September to March), since we note that
self-initiated lightning at the GBT occurred predominantly (79% or
142/179) during non-convective season. On the other hand the majority
(85% or 22/26) of nearby-lightning-triggered upward flashes at the GBT
occurring during convective season (April to August) and 80
nearby-lightning-triggered upward flashes out of 81 upward flashes
observed at the ten tall towers in Rapid City in South Dakota of USA
occurring during summer seasons, could be due to the result of high
altitude of charge region. The triggering flashes were detected to be
within 1 and 18 km distance and the time intervals between them and
upward lightning initiation are in the range of 0.3 to 90.7 ms.
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.
Towers on mountaintops have more incidence of lightning than towers on the flat ground. Therefore towers on mountaintops are ascribed an effective height that is often considerably larger than the physical height of the tower.In this paper, we review and evaluate the definitions and methods that could be used to estimate the effective height of a given tower on mountaintop and propose a new definition based on an engineering model of lightning attachment. The results can be useful in designing lightning protection of communication/transmission lines and masts on mountaintops.
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