US researchers have developed a new way to create glowing orbs of plasma similar to ball lightning in the lab, allowing them to study their chemical and physical properties. The work could help scientists unravel the mysteries of this very rare natural phenomenon.
Ball lightning has been known for millennia, but its rarity and short lived nature – typically lasting between 1 and 10 seconds – has prevented it from being studied and understood. In recent years, however, lab experiments that mimic ball lightning have been developed.
One method involves a glowing discharge produced above an aqueous electrolyte solution. However, high pressure partially ionised plasmas made this way usually only lasted for milliseconds. Now, Mike Lindsay and colleagues at the US Air Force Academy have found that altering the acidity of the electrolyte solution can produce balls that last for up to 0.61 seconds, creating an opportunity to better understand them.
'It is remarkable that you can have these charges separated in a relatively stable way for relatively long periods of time,' says Lindsay. 'The fact we can increase it from milliseconds to seconds – that's three orders of magnitude – and if one understood this further perhaps this could turn into something more substantial and usable.'
By using high-speed video cameras and infrared absorption spectroscopy the team were able to investigate the internal density and structure of such plasmoids for the first time. They found that ionised water clusters appear to be the main source of the plasma.
'There have been several previous papers on this type of plasma phenomenon, but this paper gives more details and confirms the previous reports,' comments John Lowke, who investigates ball lightning at CSIRO in Sydney, Australia. 'There is at least one observation claimed to be ball lightning that I know of, for which the present experiment would be an explanation.'
However, Lowke says the work does not explain many observations of ball lightning, including reports of seeing it pass through windows and existing inside aeroplanes. 'Most reports of ball lightning have the balls drifting above the ground, but not rising like a hot air balloon, and being quite separate of any liquid or electrolyte.'
Lindsay agrees that the lab-based phenomenon cannot explain all ball lightning observed in nature. He suggests that instead of ball lightning being one particular phenomenon it's more likely to be a series of phenomena that appear similar but are chemically and physically distinct.
The researchers are now looking at ways of extending the lifetime of the plasma and to increase the resolution and sensitivity of the spectroscopy. 'That should allow us to pinpoint exactly what molecular species are present in the plasma and then we should be able to map out its chemistry.'