Return stroke peak current versus charge transfer in rocket-triggered lightning (original) (raw)
Related papers
Characterization of return-stroke currents in rocket-triggered lightning
Journal of Geophysical Research, 2009
1] We present a statistical analysis of the salient characteristics of current waveforms for 206 return strokes in 46 rocket-triggered lightning flashes. The flashes were triggered during a variety of experiments related to the interaction of lightning with power lines that were conducted from 1999 through 2004 at the International Center for Lightning Research and Testing at Camp Blanding, Florida. The return-stroke current, after measurement, was injected into either one of two test power lines or into the Earth near a power line via a grounding system of the rocket launcher. Statistical information is presented for return-stroke peak current, charge transfer, half-peak width, and 10%-90% risetime. Our return-stroke peak current statistics are found to be generally consistent with those reported from other triggered-lightning studies and appear to be independent of electrical properties of the strike object, as previously found in another study. We found significant correlation (R 2 = 0.76) between lightning return-stroke peak current and the corresponding charge transfer within 1 ms after return-stroke initiation. The dependence is surprisingly similar to that found by Berger and co-workers for the natural first return-stroke peak currents and 1-ms charge transfers. The means of the 10%-90% current risetimes for strikes to the power line (geometric mean 1.2 ms) and for strikes to the Earth (geometric mean 0.4 ms) are significantly different which indicates that the electrical properties of the strike object affect the risetime. This effect is likely related to the impedance seen by lightning at the strike point and/or to reflections at impedance discontinuities within the strike object, larger effective impedances apparently resulting in larger risetimes. A dependence of the return-stroke current half-peak width on the electrical properties of the strike object was not observed in our direct and nearby-strike experiments.
Leader/return-stroke-like processes in the initial stage of rocket-triggered lightning
Journal of Geophysical Research, 2006
Linear streak film, video, current, and electric field records from nine triggeredlightning flashes are analyzed to examine the process of cutoff and reestablishment of current during the initial stage of rocket-triggered lightning. All of the data were acquired at the International Center for Lightning Research and Testing at Camp Blanding, Florida, in 2002 and 2003. It is shown that in some rocket-triggered lightning events, the process of current cutoff and reestablishment during the initial stage is similar to a leader/return-stroke sequence, although the currents in this process are typically an order of magnitude smaller (1 kA or so) than those in a triggered or natural lightning subsequent stroke (10-15 kA). The events were separated into two groups based on observed characteristics, with the duration of the current cutoff interval being the primary differentiating characteristic. In some cases, two or three failed attempts at current reestablishment prior to the successful resumption of current flow in the channel were observed. Currents associated with the unsuccessful attempts were typically an order of magnitude smaller (100 A or so) than in the process which finally reestablished the current.
Estimation of input energy in rocket-triggered lightning
Geophysical Research Letters, 2006
1] Electric fields in the immediate vicinity (within 0.1 to 1.6 m) of the triggered-lightning channel were measured with Pockels sensors at the International Center for Lightning Research and Testing at Camp Blanding, Florida. These fields and the associated currents measured at the base of a 2-m strike object were used to compute the input power and energy, each per unit channel length and as a function of time, associated with return strokes in rockettriggered lightning. In doing so, we assumed that the vertical component of the electric field at horizontal distances of 0.1 to 1.6 m from the lightning attachment point is not much different from the longitudinal electric field inside the channel (Borovsky, 1995). The estimated mean input energy over the first 50 ms or so is between 10 3 and 10 4 J/m, consistent with predictions of gas dynamic models, but one to two orders of magnitude smaller than Krider et al.'s (1968) estimate for a naturallightning first stroke, based on the conversion of measured optical energy to total energy using energy ratios observed in laboratory long-spark experiments. The mean channel radius and resistance per unit channel length at the instance of peak power are estimated to be 0.32 cm and 7.5 W/m, respectively. Citation: Jayakumar, V.
Journal of Geophysical Research, 2005
1] Vertical electric field waveforms due to dart leader/return stroke sequences measured on the ground 15 and 30 m from the negative lightning channel are used to examine the so-called residual electric field, the difference between the leader electric field change, and the following return stroke electric field change. At these distances, no residual field is expected if the return stroke neutralizes essentially all the charge deposited by the leader within a few hundred meters above ground. There is a clear tendency for strokes having larger peak currents to be associated with larger residual electric fields. The ratio of residual electric fields at 15 and 30 m suggests that the residual field varies as r À1.5 , where r is the horizontal distance from the lightning channel. The residual electric field is found from modeling to be associated with an equivalent point charge of the order of hundreds of microcoulombs to a few millicoulombs at a height of 15 to 30 m deposited by the leader but presumably left unneutralized by the return stroke. This residual point charge decays exponentially on a timescale of the order of milliseconds to tens of milliseconds. While the nature of the residual charge is unknown, it could be associated with small branches formed near the descending leader tip just prior to or during the attachment process. In long laboratory spark experiments, such branches have apparently been observed to lose their connection with the main channel. Citation: Rakov, V. A.(2005), Close electric field signatures of dart leader/return stroke sequences in rocket-triggered lightning showing residual fields,