First described in 1971, the Madden-Julian Oscillation (MJO) is an area of atmospheric disturbance in the Tropics, characterized by a dipole of suppressed and enhanced convection (precipitation) that propagates eastward throughout the year; depending on its forward velocity, this "wave" circles the globe every 30 to 60 days. Like other oceanic oscillations, its intensity varies from year to year.
Interacting with other atmospheric disturbances, this Oscillation affects monsoon patterns and the development of tropical storms; depending on its position at any given time, the MJO may fuel or suppress tropical storm activity (see Tropical Storm Dynamics). Acting in concert with atmospheric troughs and ridges to its north, the Oscillation may also feed bands of heavy precipitation (such as the Pineapple Express).
The current outbreak of hurricanes in the Eastern Pacific is thought to reflect interaction between the El Nino and Madden-Julian Oscillations. Relatively quiescent early in the summer, the East-Pac Hurricane Season has become especially active in recent weeks.