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The influence of the corona space charge layer created at ground level on lightning attachment to high (20–100 m) slender objects is numerically studied. The shielding effect of corona space charge produced near the object tip on the electric field at ground level is considered. The behavior of a non-stationary streamer-free corona developed from ground irregularities in a time-varying thundercloud electric field is discussed. The initiation of an upward leader from the tip of a high grounded object is simulated in the electric field created by a storm-cloud, approaching downward leader and space charge produced by corona at ground level and near the object tip. The corona space charge produced on the ground surface is shown to affect only slightly the inception of an upward connecting leader from the object when the local electric field near the object tip rises rapidly due to an approaching downward leader. The effect of neutral aerosol particles on lightning attachment to high grounded slender objects is also small. [ABSTRACT FROM AUTHOR]

Six downward negative flashes terminated on tall structures in Guangzhou are analyzed. The three-dimensional (3-D) lightning channels are reconstructed from dual-station optical observations. For each reconstructed 3-D upward connecting leader (UCL) channel, its 3-D length and speed are calculated. The 3-D length values of the six positive UCLs range from 180 to 818 m. There are 38 3-D speed values which are calculated combining the 3-D UCL channel and the high-speed images for the six UCLs. The 3-D speed values range from 0.8 to 14.3 × 10 5 m s − 1 and four of them (11%, 4/38) are on the order of 10 6 m s − 1 . For comparison, the corresponding two-dimensional (2-D) parameters are calculated using the single-station high-speed images. The values of the 2-D length and 2-D speed range from 147 to 610 m and 0.3 to 10.6 × 10 5 m s − 1 , respectively. From the statistical analysis, we determine that the average value of the 3-D speed is 1.3 times that of the 2-D speed. When the time is approaching the return stroke (RS), the propagation speed of the UCL is increasing. All of the four 3-D speed values on the order of 10 6 m s − 1 occur less than 0.2 ms prior to the RS. When the 3-D length is shorter than 300 m, 77% (20/26) of the corresponding 3-D speed values are smaller than 5 × 10 5 m s − 1 . When the 3-D length is longer than 300 m or the UCL tip height is higher than 650 m, all of the corresponding 3-D speed values are faster than 5 × 10 5 m s − 1 . [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]