When two storms meet, they perform a celestial dance of destruction
In short: When two cyclones drift too close, they don't just collide; they begin to orbit one another like celestial bodies. This meteorological phenomenon, known as the Fujiwhara effect, can cause storms to merge, stall, or dramatically alter their paths, creating unpredictable patterns of atmospheric power.
When two adjacent cyclonic vortices orbit one another, the Fujiwhara effect happens as their low-pressure cores draw closer. The interaction is dictated by the wind circulations: in the Northern Hemisphere, the systems orbit each other counterclockwise, while in the Southern Hemisphere, they rotate clockwise. The dynamics depend heavily on relative size. If the vortices are roughly equal, they engage in a 'dance' where they orbit a central point between them. However, if one is significantly larger, it dominates the interaction, forcing the smaller vortex to circle around it.
The mechanism of this interaction is still a subject of scientific discussion, with researchers debating whether it is driven by the divergent portion of the wind or vorticity advection. Distance thresholds for this phenomenon differ by storm category: tropical cyclones usually link up at 1,400 kilometres (870 mi), whereas extratropical cyclones join in binary pairs at 2,000 kilometres (1,200 mi). As they draw closer, the rotation rates accelerate; for tropical cyclones, this happens notably when they are within 650 kilometres (400 mi) of each other, with a high probability of merging occurring once they are within 300 kilometres (190 mi).
While the effect is a known meteorological principle, the final merging of two storms is relatively uncommon. Historical instances include the 1995 interaction where Hurricane Iris absorbed Hurricane Humberto, and the 2009 'dance' between Typhoon Parma and Typhoon Melor, which caused Parma to stall near the Philippines. The effect was first formally described by Japanese meteorologist Sakuhei Fujiwhara in a 1921 paper based on 1889 water tank experiments by Diro Kitao. Originally defined specifically as the merging of cyclones, the modern definition has expanded to encompass the general interaction between any two nearby cyclonic systems.
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Sources
- Summary by Intellect · source: Fujiwhara effect
- Also: Wikidata — Fujiwhara effect · CC0
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