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1.
D. Wang N. Takagi T. Watanabe V.A. Rakov M.A. Uman K.J. Rambo M.V. Stapleton 《Atmospheric Research》2005,76(1-4):412
A comparative analysis has been performed of the channel-base current and light waveforms for four rocket-triggered lightning strokes. It has been found that the current and light signals at the bottom of the channel exhibit a linear relationship (direct proportionality) in their rising portions. However, just after the peaks the linearity disappears, and the light signals usually decrease faster than the currents during the next several microseconds. Later, this trend is reversed and in some cases the light signals show another rising trend, even when the currents continue to decrease. The linear light/current relationship for the rising portions of the waveforms appears to be the same for different strokes. The findings support the idea of evaluating the variation of return stroke current along the lightning return stroke channel using light signals, provided that evaluation is limited to the rising portions of those signals and assuming that the light/current relationship observed at the bottom of the channel holds at other heights. 相似文献
2.
Triggered-lightning properties inferred from measured currents and very close electric fields 总被引：1，自引：0，他引：1
V. Kodali V.A. Rakov M.A. Uman K.J. Rambo G.H. Schnetzer J. Schoene J. Jerauld 《Atmospheric Research》2005,76(1-4):355
Triggered-lightning properties, including dart-leader charge density, return-stroke propagation speed, dart-leader electric potential, dart-leader propagation speed, and dart-leader current, inferred from return-stroke current and very close electric field measurements, are presented. Although most of the estimates are based on relatively crude models, they are all generally in good agreement with independent measurements and/or theoretical considerations found in the literature. The results are likely to be applicable to subsequent strokes in natural lightning. 相似文献
3.
We examined microsecond- and submicrosecond-scale pulses in electric field records of cloud and cloud-to-ground lightning discharges acquired in summer 2006, in Gainesville, Florida. A total of 12 cloud and 12 ground flashes were analyzed in detail, with the electric field record length being 96 or 200 ms and sampling interval being 4 or 10 ns. The majority of pulses in both cloud and ground discharges analyzed in this study were associated with the initial breakdown process and were relatively small in amplitude and duration. The typical durations were an order of magnitude smaller than tens of microseconds characteristic of “classical” preliminary breakdown pulses. We estimated that 26% of the pulses in the 12 cloud discharges and 22% of the pulses in the 12 cloud-to-ground discharges had total durations less that 1 µs. 相似文献
4.
Vernon Cooray Joseph Dwyer V. Rakov Mahbubur Rahman 《Journal of Atmospheric and Solar》2010,72(11-12):848-855
Radiation with energies up to about 250 keV associated with the dart leader phase of rocket-triggered lightning were reported by Dwyer et al. (2004). The mechanism of X-ray generation by dart leaders, however, is unknown at present. Recently, Cooray et al., in pressPlease provide complete bibliographic details for Ref. cooray e al., in press and Saleh et al., in press if available., Cooray et al., 2009a developed physical concepts and mathematical techniques necessary to calculate the electric field associated with the tip of dart leaders. We have utilized the results of these calculations together with the energy dependent frictional force on electrons, as presented by Moss et al. (2006), to evaluate the maximum energy an electron will receive in accelerating in the dart-leader-tip electric field. The main assumptions made in performing the calculations are: (a) the dart leader channel is straight and vertical; (b) the path of the electrons are straight inside the channel; and (c) the decay of the channel temperature is uniform along the length of the dart leader. In the calculation, we have taken into account the fact that the electric field is changing both in space and time and that the gas in the defunct return stroke channel is at atmospheric pressure and at elevated temperature (i.e. reduced gas density). The results of the calculation show that for a given dart leader current there is a critical defunct-return-stroke-channel temperature above which the cold electron runaway becomes feasible. For a typical dart leader, this temperature is around 2500 K. This critical temperature decreases with increase in dart leader current. Since the temperature of the defunct return stroke channel may lie in the range of 2000–4000 K, the results show that the electric field at the tip of dart leaders is capable of accelerating electrons to MeV energy levels. 相似文献
5.
The Physics of Lightning 总被引：1，自引：0，他引：1
V. A. Rakov 《Surveys in Geophysics》2013,34(6):701-729
An overview of the physics of cloud-to-ground lightning is given, including its initiation, propagation, and attachment to ground. Discharges artificially initiated (triggered) from natural thunderclouds using the rocket-and-wire technique are discussed with a view toward studying properties of natural lightning. Both conventional and runaway breakdown mechanisms of lightning initiation in thunderclouds are reviewed, as is the role of the lower positive charge region in facilitating different types of lightning. New observations of negative-leader stepping and its attachment to ground are compared to similar processes in long laboratory sparks. The mechanism and parameters of compact intracloud lightning discharges that are thought to be the most intense natural producers of HF-VHF (3–300 MHz) radiation on Earth are reviewed. The M-component mode of charge transfer to ground and its difference from the leader/return-stroke mode are discussed. Lightning interaction with the ionosphere and the production of energetic radiation (X-rays and gamma radiation) by cloud-to-ground leaders are considered. 相似文献
6.
7.
L. T. Rakov 《Geochemistry International》2006,44(10):1004-1014
Mechanisms of the incorporation of isomorphic impurities of Al, Ti, and Ge into quartz were studied by EPR techniques. For
this purpose, laboratory experiments were carried out on quartz annealing, which allowed us to model the processes of impurity
atom introduction into the quartz lattice. The investigation of the kinetics of these processes showed that they are described
by diffusion-controlled reactions. In many samples, a proportional relationship was observed between the concentrations of
Al and Ti impurities incorporated into the quartz structure during laboratory annealing. A comparison of the experimental
results with the character of the natural distribution of isomorphic impurities in quartz revealed their similarity. Based
on the analysis of the results of our investigations, two main mechanisms were proposed for isomorphic substitutions in quartz.
One of them is referred to as the capture mechanism and corresponds to the incorporation of isomorphic impurities during mineral
formation. The second, diffusion mechanism operates after the crystallization of quartz. The isomorphic impurities incorporated
into the quartz structure by this mechanism are either formed through the decomposition and transformation of composite complexes
or as a result of diffusion from crystalline and gas-liquid inclusions. It was suggested that both mechanisms are responsible
for the incorporation of Al and Ge impurities into the mineral lattice, whereas Ti is introduced mainly by the diffusion mechanism.
The accounting for the mechanisms of isomorphic substitutions provides a means to significantly increase the reliability of
the interpretation of genetic information recorded in the distribution of structural impurities in quartz.
Original Russian Text ? L.T. Rakov, 2006, published in Geokhimiya, 2006, No. 10, pp. 1085–1096. 相似文献
8.
The principal results of triggered-lightning experiments conducted at the International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, Florida, from 1993 through 2002 are reviewed. These results include (a) characterization of the close lightning electromagnetic environment, (b) first lightning return-stroke speed profiles within 400 m of ground, (c) new insights into the mechanism of the dart-stepped (and by inference stepped) leader, (d) identification of the M-component mode of charge transfer to ground, (e) first optical image of upward connecting leader in triggered-lightning strokes, (f) electric fields in the immediate vicinity of the lightning channel, (g) inferences on the interaction of lightning with ground and with grounding electrodes, (h) discovery of X-rays produced by triggered-lightning strokes, (i) new insights into the mechanism of cutoff and reestablishment of current in rocket-triggered lightning. Selected results are discussed. 相似文献
9.
Vernon Cooray Mahbubur Rahman Vladimir Rakov 《Journal of Atmospheric and Solar》2009,71(17-18):1877-1889
Different approaches are used in estimating the global production of NOx by lightning flashes, including field measurements carried out during thunderstorm conditions, theoretical studies combining the physics and chemistry of the electrical discharges, and measurements of NOx yield in laboratory sparks with subsequent extrapolation to lightning. In the latter procedure, laboratory data are extrapolated to lightning using the energy as the scaling quantity. Further, in these studies only the return strokes are considered assuming that contributions from other processes such as leaders, continuing currents, M components, and K processes are negligible. In this paper, we argue that the use of energy as the scaling quantity and omission of all lightning processes other than return strokes are not justified. First, a theory which can be used to evaluate the NOx production by electrical discharges, if the current flowing in the discharge is known, is presented. The results obtained from theory are compared with the available experimental data and a reasonable agreement is found. Numerical experiments suggest that the NOx production efficiency of electrical discharges depends not only on the energy dissipated in the discharge, but also on the shape of current waveform. Thus, the current signature, can influence extrapolation of laboratory data to lightning flashes. Second, an estimation of the NOx yield per lightning flash is made by treating the lightning flash as a composite event consisting of several discharge processes. We show that the NOx production takes place mainly in slow discharge processes such as leaders, M components, and continuing currents, with return strokes contributing only a small fraction of the total NOx. The results also show that cloud flashes are as efficient as ground flashes in NOx generation. In estimating the global NOx production by lightning flashes the most influencing parameter is the length of the lightning discharge channel inside the cloud. For the total length of channels inside the cloud of a typical ground flash of about 45 km, we estimate that the global annual production of NOx is about 4 Tg(N). 相似文献
10.
A reliable criterion of quartz genesis is proved to be ratios of the concentrations of structural defects in this mineral,
which are a function of its structural dynamic state. Within the scope of the theory of sparring defects, theoretical dependences
were derived for concentrations of various minor components accommodated in the quartz structure during two stages of isomorphism.
It was determined that structurally dynamic equilibrium may be established in quartz with time and this equilibrium “obliterates”
genetic information on the crystallization conditions. The conclusions obtained in this research are confirmed by data on
pervasively occurring relations between the distributions of isomorphous components in quartz samples from rare-metal deposits
of various genetic types. 相似文献