Super typhoons in winter are more likely to occur when the solar cycle is amplified by atmospheric and ocean interactions, National Taiwan Normal University researchers said on Tuesday.
Wu Chau-ron (吳朝榮), a professor at the university’s Department of Earth Science, said his team found that solar activity could induce typhoons or even super typhoons in the off-season, despite the lower sea surface temperature.
The study, which was jointly conducted by Wu’s team and a team led by Yu Jin-yi (余進義), professor of Earth System Science at the University of California, Irvine, collected tracking data for 402 off-season super typhoons in the western North Pacific from 1945 to 2018.
Photo: CNA
Based on their findings, the occurrence of super typhoons outside the normal typhoon season can result in devastating loss of life and property damage, Wu said.
An example of this type of super typhoon was Typhoon Haiyan in 2013, Wu added.
The study looked into the three conditions that enhance the chance of off-season typhoons occuring, the first being the solar cycle, Wu said.
Every 11 years, the sun’s magnetic poles change their polarity, and the Earth gains more momentum, heating up the tropopause, which causes the Hadley cell and northeast trade winds to weaken, he said.
Second, atmospheric conditions, such as global warming, strengthen the connection between subtropical and tropical zones, which increases the relationship between the solar cycle and the formation of typhoons, Wu said.
Third, the ocean-atmosphere interaction heats up the northeastern Pacific and that warmth reaches the central Pacific, which reduces the Walker cell and results in deep ocean circulations moving east, he said.
Such interaction also weakens the vertical wind shear in a way that facilitates the formation of off-season typhoons, he added.
As typhoons are formed further east in the off-season and there is a lack of steer flow, they move more slowly, which means more energy and water are absorbed from the ocean, increasing the probability of a super typhoon forming, Wu said.
As the Earth faces an active solar period over the next two years, the likelihood of super typhoons occurring is greater and people should be vigilant, he said.
The study was published in the npj Climate and Atmospheric Science journal on Oct. 20.
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