Typhoon Haiyan was already one of the strongest tropical storms on record. Now it has another claim to fame.
Analysis of satellite data has revealed that the storm, which hit the Philippines in 2013, hosted a spectacular lightning show in its innermost core – something not seen in recorded storms of similar intensity.
Haiyan was found to have lightning at its core for 49 per cent of its life between 3 and 11 November that year, when it killed some 6300 people and wreaked huge damage to property and infrastructure. By comparison, hurricanes Rita and Katrina had lightning at their cores for just 5 and 3 per cent of their existence, respectively.
“Lightning is usually infrequent in the inner core [of a storm],” says Wenjuan Zhang at the Chinese Academy of Meteorological Sciences in Beijing. “Normally, lightning is found at the periphery of storms.”
Zheng presented her findings on 24 April in Vienna, Austria, at the annual meeting of the European Geosciences Union. They arise from an analysis of data on the lightning from space satellites, as well as from 70 stations on the ground that comprise the World Wide Lightning Location Network.
She added that tracking lightning from space may turn out to be another way to monitor and predict the intensity of storms. “Lightning may be a proxy for intense convection,” she says. But more research is needed to see if this is really the case.
Zhang’s analysis showed that the core lightning occurred in three stages of Haiyan’s life: as it intensified rapidly in the west Pacific; at the point of its maximum intensity; and towards the end of its life, as it veered away from the Philippines towards the Asian mainland.
She also found that the conditions where Haiyan formed were perfect for lightning to evolve, with unusually warm seas, high humidity and low crosswinds.
These factors enabled the formation of high “tower” clouds, which accumulate positive and negative ions at different heights – almost like an enormous battery. With large areas of opposite charge building up within clouds, lightning strikes between clouds and down to the ground were abundant.
The other striking thing, says Zhang, was that the lightning in the first two phases coincided with a storm formation that remained almost perfectly symmetrical when viewed from above. This may have been a further factor in focusing the lightning in the eye of the storm, she says, though it’s not yet clear if this was the case.
Only in the final phase did the symmetry disappear. But the core lightning re-emerged as Haiyan veered north, possibly because of changes in the interaction of crosswinds and storm movement.