The storm king

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Science  02 Oct 2015:
Vol. 350, Issue 6256, pp. 22-25
DOI: 10.1126/science.350.6256.22

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A mysterious weather pattern stalks Earth's tropics. Every 30-60 days, something called the Madden-Julian oscillation (MJO) circles the equator, bringing rain and wind wherever it goes. Discovered in 1971, but still not completely understood, the MJO is the biggest driver of tropical weather. It also has large effects on weather outside the tropics, triggering and strengthening hurricanes, monsoons, and heat waves in higher latitudes. This year's powerful El Nino was almost certainly set off by a trifecta of MJO events. Scientists are making progress in understanding this hidden force in weather and climate. Computer models are finally mimicking the MJO, after decades of failure. That is allowing weather forecasters to push their predictions further into the future than ever before, while climate scientists are exploring how the MJO will behave in a warmer world. And after an intense field campaign in the Indian Ocean involving dozens of nations, researchers are starting to answer some of the most fundamental questions of all: Why does the MJO exist, and how does it form?