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The 2012 spectrum

In a paper published on 17 January 2014, Jianyong Cen, Ping Yuan and Simin Xue reported that ball lightning was observed with two slitless spectrographs at a distance of 0.9 km. PRL 2014 The ball lightning, they write, is generated by a cloud-to-ground lightning strike, and it moves horizontally during the luminous duration. PRL 2014

The event occurred during a thunderstorm at 21:54:59 on 23 July 2012 (Beijing Time), on the Qinghai Plateau of China. PRL 2014 The entire luminous duration of the ball lightning was 1.64 s. PRL 2014 They report that it moves horizontally with an average 2D speed of about 8.6 m/s, and that the actual speed should be faster than the 2D speed if it also moved in the line-of-sight direction. PRL 2014

The colours of purple, orange, white, and red can be seen in turn during the luminous duration: powerful purple white at the beginning, orange at 80 ms, approximately white from 160 to 1100 ms, and red at the dissipating stage after 1120 ms. PRL 2014

A reminder that one 2012 event was recorded with spectrographs, which showed lines from soil elements. This is our own diagram, not the original spectrum.Drawing: our own, simplified and not to scale

The spectral analysis indicates that the radiation from soil elements is present for the entire lifetime of the ball lightning. The emission lines of silicon, iron, and calcium appeared, and silicon, iron, and calcium are the main components of soil. PRL 2014 The authors write that there are reasons to believe that the observed ball lightning was generated by the cloud-to-ground lightning striking to the soil on the ground. PRL 2014

They warn that the apparent diameter is not the real diameter of the ball lightning. This site does not treat the apparent-diameter figures in that paper as the object’s true size. PRL 2014

They also write that there may be more than one type of ball lightning and more than one mechanism that explains it, and that their observation is only one event that may not be representative of all ball lightning. PRL 2014

This is still one event, recorded 0.9 km away, not a complete theory of every glowing sphere people have reported. It is, though, a rare case with spectra, timing and a clear link to a cloud-to-ground strike.