Fujiwhara effect

The Fujiwhara effect, sometimes referred to as the Fujiwhara interaction or binary interaction, is a phenomenon that occurs when two nearby cyclonic vortices move around each other and close the distance between the circulations of their corresponding low-pressure areas. The effect is named after Sakuhei Fujiwhara, the Japanese meteorologist who initially described the effect. Binary interaction of smaller circulations can cause the development of a larger cyclone or cause two cyclones to merge into one. Extratropical cyclones typically engage in binary interaction when within 2,000 kilometres (1,200 mi) of one another, while tropical cyclones typically interact within 1,400 kilometres (870 mi) of each other. Fujiwhara described the effect in a 1921 paper which was based in an 1889 paper by a Japanese researcher and eventually gained popularity in the United States after World War II.