The Fujiwhara effect, sometimes referred to as Fujiwara interaction or binary interaction, is when two nearby cyclonic vortices orbit 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 1,200 miles of one another, while tropical cyclones typically interact within 870 miles of each other.