The solar wind must be strong
tonight (Image: Getty Images)
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By all accounts, lightning
should be impossible. Air is an electrical insulator, so getting it to
conduct current requires an incredibly intense electrical field. The puzzle is
that observations of thunderstorms show that their fields
are much too weak for bolts to fly,
says Christopher Scott at the University of Reading, UK.
idea is that high-energy particles from outer space called cosmic rays might
provide the necessary boost. When incoming particles
collide with air molecules, they set electrons loose and
ionise the air, creating a cascade that lets current
theory hasn't been fully confirmed. But if the mechanism holds, Scott and his
colleagues think they have found another extraterrestrial
trigger: the sun. Charged particles emitted by the sun, known as the solar
wind, blast Earth at regular intervals, with a peak every 27 days or so.
solar wind has its own magnetic field, and during a peak this field
deflects about 1 per cent of incoming cosmic rays from
hitting Earth. At the same time, the number of solar particles reaching Earth
increases by 6 per cent. If solar particles ionise the air in the same way as
cosmic rays, the net effect should be an increase in lightning strikes during a
peak in solar wind strength, says Scott.
test this idea, the team compared data from the Advanced Composition Explorer
(ACE) spacecraft, which measures the solar wind, with lightning rates seen
between 2000 and 2005, as measured by monitoring stations for the UK Met Office.
In the 40 days after a blast of solar wind, the UK saw an average of 422
lightning strikes. By contrast, there were 321 strikes
on average in the 40 days before a blast.
solar wind peaks regularly, and its cycles are measured by spacecraft like ACE.
That means it should be possible to predict dangerous storms, says Scott.
"Lightning is one of the major meteorological hazards. I
think it is up there with flooding and mudslides for killing people worldwide,"
That's not to say solar particles will turn a calm day
misery, because storm conditions already have to be in place to spark
effects of solar wind are limited, if this paper is true, to making lightning
happen more often, providing conditions are already
conducive to lightning," says Christopher Emersic at the University of
also notes this point, but he adds that if a thunderstorm is coming,
meteorologists might be able to use data on the solar wind to predict how severe
a storm is going to be.
result also doesn't make it clear how lightning is created in the first place,
says Joseph Dwyer at the Florida Institute of Technology in Melbourne. "The
paper finds that conditions in outer space are somehow affecting the production
of lightning in thunderstorms. This is a very puzzling result, since it is
not obvious how the two are connected," says Dwyer. "However, scientists still
do not understand how lightning is initiated inside thunderstorms, so perhaps
this work is providing a clue."
Journal reference: Environmental
Research Letters, DOI: 10.1088/1748-9326/9/5/055004
Source: New Scientist URL: