For six decades, scientists have watched a steadily circulating wind pattern in the tropical stratosphere, repeating like clockwork every two years. Now, for the first time, it's changed direction.
The pattern is called the quasi-biennial oscillation and it's a wind circulation that occurs every 28 months, miles above Earth's surface in the stratosphere. West-moving winds from the top of the tropical stratosphere slowly move downwards and are replaced in that top position by the easterly winds that were below them. Then the whole switch occurs repeats itself again and again, for the last 60 years at least.
But at the end of last year, right when the west-moving winds were supposed to be moving down to start the switching pattern, instead, they rose right back upwards. The new pattern held for a full six months before the east winds finally replaced them again at the top this July.
Researchers from NASA Goddard revealed the change in a paper in Geophysical Research Letters. The switch hasn't yet had any visible impact on existing weather patterns — besides the shift in wind circulation — but the sudden change still has scientists surprised and searching for an explanation. "The quasi-biennial oscillation is the stratosphere's Old Faithful," Paul Newman, lead scientist on the paper from NASA Goddard said in a statement. "If Old Faithful stopped for a day, you'd begin to wonder about what was happening under the ground."
Newman suggested two potential theories that could explain the switch. One is that it was yet another strange side-effect from the gigantic El Niño we just saw. But he also suspects that it could be an effect of our new, hot climate. The researchers are now trying to figure out just what the impact of the switch might be — and whether, as the world continues to warm, we're going to see it happen again.