Science: In 1971, meteorologists Roland Madden and Paul Julian studied weather data from near-equatorial Pacific islands. To their surprise, tropospheric winds, pressure, and rainfall oscillated with a period of about 40 to 50 days. The oscillation in clouds and precipitation tends to be confined to the tropical Indian and Pacific oceans, but the oscillation in winds and pressure is felt throughout the tropics. The search for a single robust theory for this Madden-Julian Oscillation (MJO) continues today.

The MJO is not a true oscillation, in the sense that its period varies and its appearance is episodic, but it is the largest source of tropical weather variability on subseasonal time scales, especially in the Indian and Pacific oceans. In last week's Science Matthews et al. use observations from the new Argos system of profiling floats to reveal the deep-ocean response to the MJO. Also in the same issue, Miura et al. report an advance in modeling the MJO.