Typhoons and hurricanes are names for the same kind of tropical
cyclone. Stronger than a
subtropical storm both are defined as having a maximum sustained surface wind speed of 74 mph. The term
typhoon applies to cyclones in the western Pacific Ocean.
Meteorologists use the word
hurricane when talking about cyclones in the
Atlantic Ocean and certain parts of the Pacific Ocean. In the region of
Australia and in the
Indian Ocean, they refer to these storms as just cyclones.
There's also an unusual expression for a "dance of cyclones" described when two of them slowly rotate around a common midpoint, that's called the "Fujiwara effect." This effect or interaction usually occurs when tropical cyclones or typhoons meet and start to rotate around a central point, kind of like two ice skaters locking arms and spinning in dance together. It only seems to happen when the two storms are the same size.
Many sources define it simply as “the rotation of two storms around each other." the Fujiwara Effect is better defined in the glossary prepared by the Bureau of Meteorological Research Centre in Australia as an:
Interaction of two binary cyclones in which both orbit cyclonically about their geometric centre; named after the pioneering laboratory experiments of Fujiwhara (1921).
Also known as
binary interactions, sometimes the Fujiwara effect can be applied to the interactions between two, three, or four tropical cyclones within defined distances of each other and the manner in which these tropical cyclones either attract or repel each other.
When hurricanes collide within a certain distance, usually 300-750 nautical miles depending on the sizes of the cyclones, it’s also called the Fujiwara dance or the Fujiwara waltz. This easily adaptable metaphor is an eponym from Dr. Sakuhei Fujiwhara who was the Chief of the Central Meteorological Bureau in Tokyo, Japan shortly after the World War I.
In 1921 Fujiwhara wrote a paper relating the activity of "vortices" in water. Water vortices are little water whirls that spin around. One example of a water vortex is a whirlpool. Fujiwhara studied these vortices closely and noted that that if two vortices were identical in size and strength and spin in the same direction; for example, counter-clockwise, they would travel about each other as defined above. But he also noticed other movements and made several observations:
- When two vortices spinning counter-clockwise draw near and one of the vortices is bigger than the other, they start spinning around each other for a brief time with the larger one dominating. Gradually the lesser of the two gets trapped in the circulation of the larger one and absorbed.
- When comparable vortices spin in opposite directions, one clockwise, one counter-clockwise, they press each other away when they near.
Fujiwara is a variant of Fujiwhara and can be found spelled either way in scientific as well as press releases. This is where the term Fujiwara effect comes from and is used most frequently when meteorologists talk about tropical cyclones. It’s interesting to note that Dr Fujiwhara was thinking about the interactions of the atmosphere well before these interactions could be observed. It wasn’t until the 1960’s that the first meteorological satellites were launched. Over most of the twentieth century, research in tropical cyclones focused more on the motion of a single vortex than that of multiple, interacting vortices. It wasn’t until the middle of the 1980s that investigations in the area of tropical cyclone interaction flourished and the first numerical simulation of tropical cyclone interaction was over 60 years after Fujiwhara's breakthrough paper. Perhaps the more mathematically inclined would like to make a nice addition to this node? (hint hint).
The Fujiwara effect is likely just about anywhere atmospheric or water vortices come close together. How often do hurricanes collide or interact with one another?
More often in the western North Pacific than in the North Atlantic, one study established, where one or two cyclone interactions happen each year, weighed against one interaction every three years in the Atlantic. The reason the Pacific has more interactions between cyclones is because on average the Pacific gets twenty-five cyclones annually versus only ten per year in the Atlantic. Cyclone interactions are broken down into four categories or steps: 1. Approach and Capture, 2. Mutual Orbit, 3. Merger and 4. Escape.
Scientists since Fujiwhara have considered the effect and believe many other developments can hamper the effect so it doesn't always occur. Still many examples like this one appears to prove Dr. Fujiwhara's findings.
When Tropical Storm Iris was approaching the Windward Islands on Aug. 23, 1995 and Hurricane Humberto was close behind, they drew close enough together to begin a Fujiwhara dance. The effect is thought to occur when storms get about 900 miles apart. As Humberto chased down Iris, Humberto began to lift northward over Iris while Iris slowed down and turned a bit to the south. Iris became a hurricane just as this "dance" began but both storms were weakened by their passion for each other. As they weakened other forces in the atmosphere broke them apart and sent them on their separate ways.
About 8 days later, Iris, now a hurricane with 110 mph winds, was moving northward east of Bermuda. This time Tropical Storm Karen scooted in behind Iris. But Karen was a much weaker storm with winds of only 45 mph. As the storms moved closer the Fujiwhara effect began. But Iris' strength dominated and poor Karen was flung around Iris to the north and Iris absorbed Karen right into its circulation while barely flinching.
Dr. Fujiwhara’s descriptions of "vortices," or whirlpools in water, guided meteorologists to relate his observations to tropical events in the atmosphere like cyclones, typhoons and
hurricanes.
Dust devils, by the way, have been found to show evidence of the Fujiwhara interactions on land.
Isn’t science amazing?
A picture of two tropical storms displaying the Fujiwara effect can be seen at
http://www.photolib.noaa.gov/historic/nws/wea00481.htm
Sources:
BMRC:
http://www.bom.gov.au/bmrc/pubs/tcguide/ch9/ch9_2.htm
Draft of Term Paper (Thesis Proposal) - Trop Cyclone Motion:
www.ems.psu.edu/~hart/tropdraft.html
Fujiwhara, S., T. Oomari and K. Taguti, "Sinkiro or the Japanese Fata Morgana," Geophys. Mag., Vol. 4, pp. 317-374 (1931).
USA Today:
http://www.usatoday.com/weather/wfujiwha.htm
When Hurricanes Collide:
www.earthsky.com/2000/esmi000609.html
yourdictionary.com:
http://www.yourdictionary.com/cgi-bin/wotd.cgi