The cloud of ash blowing south from an Icelandic volcano last month was electrically charged. It’s a finding that could be exploited to build detectors to warn pilots when they are flying into danger
Volcanic ash is deadly stuff for aircraft, and has been known to clog up engines and cause them to stall. But the disruption to European air traffic last month caused by the ash could have been reduced if pilots had an instrument that could detect ash clouds, says Giles Harrison of the meteorology department at the University of Reading in the UK.
On 19 April, when Eyjafjallajökull’s cloud hung over Europe, Harrison and his colleagues released a weather balloon carrying instruments to measure particle size and concentration, and the electrical charge in the atmosphere, from a site on the west coast of Scotland.
As the balloon entered the 800-metre-thick ash-laden layer of the atmosphere, they noted a rapid increase in particle concentration and a positive electrical charge that they say could not be attributed to local weather conditions or other sources. “We think that particle collisions must be creating the charge,” says Harrison.
The charge increased with particle concentration, reaching a maximum of around 0.5 picocoulombs per cubic metre in areas where there were 50 particles per cubic centimetre of air.
That’s around 1/20th of the concentration beyond which the UK Civil Aviation Authority (CAA) has said aircraft are not allowed to fly. “Combined with other measurements, a simple charge detector on an aircraft should be able to alert pilots to dangerous levels of ash,” says Harrison.
Whether such a system would be of practical use in busy airspace is another question. “UK airspace is very congested, so any detection system has to be able to warn of the ash far in advance, to give time to manoeuvre safely,” says a spokesperson for the CAA.
Journal reference: Environmental Research Letters, DOI: 10.1088/1748-9326/5/2/024004
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