Historical research guide · 0024 · 2014
Observation of the optical/spectral characteristics of ball lightning
Cen, Yuan · Xue
In one minute
In July 2012 a team from Northwest Normal University had two slitless spectrographs pointed at a thunderstorm on the Qinghai Plateau, studying ordinary lightning. A cloud-to-ground stroke hit the ground about 900 metres away, and a luminous ball rose out of it. Jianyong Cen, Ping Yuan and Simin Xue caught the whole event on video and, more valuably, in spectrum — the first optical spectrum of natural ball lightning anyone has recorded. The ball was roughly five metres across, drifted at about 8.6 metres per second, and lasted a little over a second and a half, shifting from purple-white through orange and white to red as it went. The spectrum answers the oldest question about the phenomenon. It carries emission lines of silicon, iron and calcium — the elements you would expect in the soil the lightning had just struck — and that soil radiation is present for the object's entire lifetime.
Connection
Chapter 9's case is that self-organising luminous plasma is ordinary physics wearing an extraordinary face, and this is the measurement that made the case: one accidental spectrum turned ball lightning from a folklore report into a dataset with named elements in it.
From the source
Ball lightning was observed with two slitless spectrographs at a distance of 0.9 km, generated by a cloud-to-ground lightning strike — the first time the phenomenon has been recorded forming directly from a stroke.Abstract; observation and instrumentation
The evolution of size, colour and light intensity is reported in detail: the ball was about 5 metres across, travelled at roughly 8.6 metres per second, lasted a little over 1.5 seconds, and changed from purple-white through orange and white to red.Results, optical characteristics
The recorded spectrum contains emission lines of silicon, iron and calcium — all elements abundant in soil.Results, spectral analysis
Radiation from soil elements is present for the entire lifetime of the ball lightning, not only at its formation.Abstract; spectral time series
The measurement supports the hypothesis that a natural luminous sphere of this kind is made from material vaporised out of the ground by the lightning stroke.Discussion and conclusions
The observation was accidental — the instruments were set up for ordinary lightning research on the Qinghai Plateau — so a second natural spectrum, captured deliberately, is the measurement the field is still waiting for.Observation circumstances, July 2012 field campaign
The way in
https://link.aps.org/doi/10.1103/PhysRevLett.112.035001How to cite it
Cen, Yuan, Xue (2014) Observation of the optical/spectral characteristics of ball lightning doi:10.1103/PhysRevLett.112.035001