Richard Musgrove
As Australians along the east coast deal with Tropical Cyclone Alfred cutting a swathe through regions which rarely get these weather events, new research shows that hurricanes in the northern hemisphere are also appearing in odd places.
Cyclones are carried along in massive rivers of air — 10km high ‘steering flows’ – Cyclone Alfred is no different, and the result is flooding across a wide area.
There have only been a handful of cyclones in this latitude in the past 100 years.
So much influences where cyclones and hurricanes form. And just like humans, where they are born effects where they head next. They all originate over warm ocean waters (at least 27oC) in the tropics or subtropics, generally at least 480km from the equator, says NOAA.
But researchers from the Chinese Academy of Sciences have revealed North Atlantic hurricanes have been spawning further south, in a zone from 10o to 20oN, each year since 1979.
And this long-term southward shift could make these deadly storms even worse for island nations and coastal North America.
Analysis of data from 39 climate models also showed that greenhouse gas emissions are to blame, says lead author, Cao.
More hurricanes are resulting from decreasing vertical wind shear at these latitudes, caused by a reduction in the north-south temperature gradient, says Cao. On a still morning a column of smoke rises vertically, until it reaches a certain height, then the top starts to get blown away; the lower parts are unaffected — that’s wind shear. Less vertical wind shear, means that hurricanes are forming more easily further south, says Cao.
“This shift could heighten the risk of hurricanes in low-latitude regions, posing greater threats to vulnerable island nations and coastal communities in North America.”
The paper was published in Climate and Atmospheric Science
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