Fujiwhara effect
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The Fujiwhara effect or Fujiwhara interaction is a type of interaction between two nearby cyclonic vortices, causing them to appear to "orbit" each other.
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[edit] Description
When the cyclones approach each other, their centers will begin orbiting cyclonically about a point between the two systems. The two vortices will be attracted to each other, and eventually spiral into the center point and merge. When the two vortices are of unequal size, the larger vortex will tend to dominate the interaction, and the smaller vortex will orbit around it.
The effect is often mentioned in relation to the motion of tropical cyclones, although the final merging of the two storms is uncommon. The effect becomes pronounced in these storms when they approach within about 1450 km (900 miles) of each other and are at tropical storm strength or stronger.
[edit] History
The effect is named after Dr. Sakuhei Fujiwhara, the future chief of the Central Meteorological Bureau in Tokyo, Japan, who initially described it in a 1921 paper about the motion of vortices in water.
[edit] Examples
A few sets of examples can be found in the busy 1995 Atlantic hurricane season. During the height of the season, Hurricane Humberto and Hurricane Iris took part in a brief Fujiwhara interaction [1]. Iris then began interacting with a third storm, Tropical Storm Karen, which orbited and later merged with the more intense Iris. In the 1994 Pacific typhoon season, Typhoon Pat and Typhoon Ruth completed a full orbit around their centroid before collapsing into a single cyclone [2].
The most recent example in Atlantic is a tropical disturbance being absorbed by Lisa in 2004. The Tropical Cyclone Report explained the situation clearly. The most recent example in Eastern North Pacific is Lidia being absorbed by Max in 2005. The most recent example anywhere in the world occurred when Tropical Storm Wukong absorbed Tropical Storm Sonamu in the 2006 Pacific typhoon season south of Japan.
