Fujiwhara effect
The Fujiwara effect or Fujiwara interaction is a type of interaction between two nearby cyclonic vortices, causing them to appear to "orbit" each other.
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.
Namesake
The effect is named after Dr. Sakuhei Fujiwara (藤原 咲平) (1884 - 1950), the Japanese meteorologist who initially described it in a 1921 paper about the motion of vortices in water.[1]
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 Fujiwara interaction.[2] 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.[3] In 1997, Ivan and Joan were a pair of super typhoons that interacted through the Fujiwara effect. The interaction affected their motion as Ivan was steered to the west, and Joan was steered more northerly.
The most recent example in the Atlantic is Alpha being absorbed by Wilma in 2005. One year earlier, Lisa absorbed a tropical disturbance as described in the Tropical Cyclone Report.[4] The most recent example in Eastern North Pacific is Lidia being absorbed by Max in 2005. Another recent example occurred when Tropical Storm Wukong absorbed Tropical Storm Sonamu in the 2006 Pacific typhoon season south of Japan. In 2007, Tropical Storm Hagibis made a recurvature in South China Sea towards Typhoon Mitag, northeast of the Philippines.