Variations in rainfall and storm intensity over a broad swath of the Southern Hemisphere follow a pattern that repeats every 20 to 30 days. The pattern is the first regular atmospheric oscillation found outside the tropics and could help scientists forecast weather and climate changes in the region.
Weather is notoriously chaotic; even the best forecasts are rarely accurate more than a week or two out. In the last century, however, long-term climate patterns have emerged from seemingly disordered data. Most famously, El Niño is a cycle of atmospheric energy over the tropical Pacific Ocean that repeats every two to seven years; the pattern, known since the early 1900s, can cause floods and droughts around the world. More recently, in 1994, researchers found the Madden-Julian Oscillation, which sends storms churning eastward across the tropics on a 30- to 60-day cycle. Until now scientists had not found similar atmospheric oscillations in higher latitudes.