SMOKE from forest fires raging in Mexico this spring mysteriously affected
lightning in the central US.
Normally, about 10 per cent of lightning is 鈥減ositive鈥�, when electrons stream
up from the Earth to clouds. These strikes are more destructive than negative
ones moving the opposite way.
However, figures from the US National Lightning Data Network show that the
fraction of positive strikes tripled during smoky periods. Walter Lyons of FMA
Research in Fort Collins, Colorado, says the smoke may affect charge development
(Science, vol 282, p 77). 鈥淏ut we don鈥檛 really understand the details,鈥�
he adds.
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