Can spontaneous synchronization of lightning flashes occur in a network of distant thunderstorms?
Writing by mustafa on Saturday, 26 of January , 2008 at 11:23 am
The proximity in time and space of consecutive lightning flashes in thunderstorms was first studied by Mazur (1982) who termed the phenomenon “associated lightning discharges”. These flashes were reported to occur in multi-cell storms, where several electrically active cells (EACs) co-exist in the same mesoscale region. VHF radar observations showed that lightning echoes from discharges follow one another within a time interval typical of a multistroke cloud-to-ground (CG) flash, but are spaced in range by several km. Mazur (1982) used statistical methods to disprove the null hypothesis that these associated discharges were merely a pooled output of randomly occurring flashes. He concluded that an association between flashes is the triggering of one flash by another flash, separated spatially from it, and suggested that the interdependence of the electric field within neighboring EACs may be the responsible mechanism.
Reports of a similar phenomenon, but on a larger scale, were obtained from astronauts in manned space missions, compiled by Vonnegut et al.(1985). They quote astronaut Edward G. Gibson who flew on the Skylab 4 mission in November 1973. After noting the fact that lightning was occurring simultaneously or almost simultaneously over wide areas and large distances, he used the phrase “sympathetic lightning bolts” to describe the repeated sequences of lightning activity. Gibson claimed that tens of lightning flashes were occurring almost together after periods of calm, and then the activity subsided for several seconds, only to resume again “in all location”. Astronaut Richard H. Truly, who flew the space shuttle missions STS-2 and 8, reported two separated areas of frequent lightning in the Amazon basin that appeared “to be talking to each other”. These and other reports suggested the existence of a possible coupling between widely separated lightning events and were among the drivers to perform space shuttle observations of thunderstorms, in what was later called the Mesoscale Lightning Experiment (MLE). The results from the MLE were discussed by Vonnegut et al. (1985) who analyzed the video images taken by the shuttle crews of STS-2, 4 and 6 missions (November 1981, June 1982 and August 1983, respectively). The authors suggested that the manner of luminosity pattern development as observed from space is caused by the release of electrical energy in one portion of the cloud, which eventually triggers the development of a new breakdown process in another part. That limited study has not supplied a conclusive mechanism to explain the observations.
When searching for Transient Luminous Events in the MEIDEX data (Israelevich et al., 2004; Yair et al., 2004, 2005a), we noticed the semi-cyclic pattern mentioned by Vonnegut et al. (1985), and clearly observed how distant thunderstorm cells seemed to “ignite” each other in a repeating sequence, with periods of quiet and diminished activity in between active ones. Lightning occurring in one region were immediately followed by lightning in other regions, separated spatially by tens or hundreds of kilometers. The time delay between the onset of a visible flash in one thunderstorm and that of the following flash in the distant active cell varied from several tens of milliseconds to a few seconds. The gaps and recurrence of lightning activity was also quite clear from the video images, and prompted us to perform a quantitative estimate of this Mesoscale phenomenon and to suggest possible generating mechanisms (Yair et al, 2005b).
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