Taiwan weather expert explains 'double vortex' on satellite map, clarifies Fujiwara effect conditions

A recent satellite image captured two swirling weather systems, prompting discussion about their interaction. Former Central Weather Bureau Director Zheng Ming-dian explained the phenomenon on social media.

Zheng pointed out that when two vortices form within the same low-pressure system, a weak convergence band often connects them, appearing as a curve linking the two swirls on satellite imagery. He noted that this visual cue is frequently observed during the Fujiwara effect.

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When two vortices form within the same low-pressure system, a weak convergence band often connects them, appearing as a curve linking the two swirls on satellite imagery.

However, Zheng emphasized that the current situation does not constitute the Fujiwara effect. The primary reason is that the main systems are not two typhoons. Furthermore, the distance between the two vortices is too great to meet the criteria for this atmospheric interaction.

The Fujiwara effect, first described by Japanese meteorologist Sakuhei Fujiwara in 1921, was initially observed in fluid dynamics experiments where two vortices would orbit each other when close. This phenomenon was later found to occur with atmospheric vortices, specifically when two typhoons or tropical cyclones approach each other, leading to a series of interactions.

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This current case cannot be called the Fujiwara effect, because the main systems are not two typhoons, and the distance between the two vortices is too far.