Home Report BL
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Sunday, 13 February 2011 10:00


Below is a description of a physical phenomenon that is identified by observers as a ball lightning event (BL) which owns all or a part of characteristics of a real BL.


Site: Pruno, (Stazzema, Lucca)

Altitude: 470 above sea level

Date: June 20, 2010

Time: Early afternoon



The meteo conditions was very bad on the morning with variable intensity rainfall, interrupted by moments of "quite". There was no wind and temperature was around 15-18 C. At a given point, early in the afternoon, he stops on a little bridge that crosses the Deglio's river that, due to heavy rains even the day before, had an exceptional flow rate. He decide to stay there to catch a short movie of the river upstream and, in particular, to frame a precise area of the river from a distance of about 20 m by using the zoom of his digital video-camera. The movie lasts about six seconds and in this short time interval, within the monochrome viewfinder, he feels something unexplained strange, but he does not give some attention. Only in the final editing of the video, he understands what was strange. In a totally random way in that shot he took over a small ball of orange light, but more white inside the nucleus, moving with irregular motion, with estimated size of a few centimeters. Within those six seconds, the object remained visible for about three seconds, maintaining a constant size and brightness, after which it suddenly vanishes. Halving the speed of the movie, in fact, it is noted that instead of vanishing abruptly the ball accelerates upwards in a diagonal line and then vertically, leaving the camera field of view. At the time of the video recording was not raining and the sky was partially covered. The witness did not receive any special smell, no sound or noise except that of the flowing river.


In particular, we have identified three frames taken from the original movie corresponding to three different positions of the ball with three different conditions of the background. Further, we performed the analysis of spatial variation of intensity of the luminous "sphere", measured along a diameter, splitting the RGB channels. Note that although the object shape is near spherical one, in the following frames, due to the video format conversion, the ball images appear slightly vertically elongated. The pixels used for the analysis of the ball was: 30x11

Frame n°1

frame sfera




Frame n° 2

frame sfera




Frame n° 3

frame sfera




We characterized the water near the ball. Note the inversion of RGB curves.



In order to better verify the behavior of RGB curves, as a function of the background, we performed a larger space analysis by placing the object at the center: The following figure shows the result of comparing the scale with those pixels in real image the film appropriately scaled for direct comparison.




  1. the RGB analysis shows that the type of light emission from the ball is not monochromatic;
  2. there is no saturation of the image;
  3. from 1) and the absence of blinking of the ball, mainly in the position related to turbulent water, would be excluded, as an explanation of the image, the projection of a laser source at a distance;
  4. the light emission of the object dominates in the red band in all positions;
  5. the detected intensity of light is emitted from the source and it is not a reflection from any kind of an external source and is almost constant;
  6. the peak intensity does not change significantly when changing the emissivity of the background: the object is not "transparent" in the visible;
  7. estimated size, motion, stability, type of light emission and the environmental high-humidity conditions, would suggest a probable ball lightning.



We analyzed the motion of the luminous ball recorded in about 2 seconds of its visibility in quasi-stationary conditions, before his sudden demise with great acceleration.

To determine the dynamics of the ball, we initially split the movie into individual frames, the frames were then aligned (stacking) isolating the image of the ball by eliminating background context.

The result is show in figure.


As we can see, from a first inspection, the ball shows a high variability in the motion with quasi-stationary periods alternated with periods of high speed. Of course, we dropped the final frames where the ball accelerates disappearing. Starting from the individual frames, we extracted the coordinates (in pixels) of the "core" of the ball and transformed into the known physical size scale reported above.

Limiting ourselves to the dynamics in the plane perpendicular to the line of sight (transverse components) the calculation of Euclidean distances, given that the interval between two successive frames is 1/25 s, led to a graph of speed shown in Figure.



Animated graph of the BL dynamics

dinamica animata



We can easily see continued acceleration and deceleration, with a few intervals at a constant speed. The peak shapes show a dynamics of ball which must be resolved well after the typical scan rate of movie: 1/25 s. Most acceleration occurs at about 1.59 s where the velocity rose from 37.5 cm/s to 180.3 cm/s in 0.04 seconds (acceleration: 3.6 g), and next reduced to 12.5 cm/s in 0.16 seconds. Here no rotation of the ball was detected.

After this analysis of the dynamics of the ball we can safely say that the type of motion and the quantitative estimates of speed, agree well with the data and current models of ball lightning.

To complete the analysis, we also performed a sound analysis: The file of environmental noise sampled at 8KHz has been subjected to a wavelet analysis to highlight the possibility, in the time of appearance of the ball, to detect a noise characteristics of the BL. However, the obtained results clearly showed no evidence of different specific frequencies from those of the ambient noise background.

Last Updated on Monday, 14 February 2011 21:39
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