What kinds of weather do the coming months hold? Highly unusual behaviour in the upper atmosphere indicates that northern Europe may be in for another stormy winter. The first sign appeared back in February, when scientists spotted something odd in high-level balloon wind measurements.
Way up in the stratosphere – 16-50km above the equator – the balloon measurements revealed a narrow band of westerly winds, tucked inside the freshly formed equatorial easterly winds.
Normally these high-level tropical winds – known as the quasi-biennial oscillation (QBO) – are either easterly or westerly, and ever since they were discovered in 1960 they have smoothly switched direction approximately every 22 to 36 months.
Meteorologists were shocked, and immediately double-checked their measurements. But everything backed up the presence of this unprecedented ripple, which has prevented the QBO from finishing its full cycle and switching back to easterly this year.
No one is sure what has caused this blip, though scientists speculate on a few possibilities in a study published in Science magazine.
Ordinarily the QBO is a useful seasonal forecasting tool, with westerly QBO winds tending to lead to more extreme pressure differences over the North Atlantic and a higher likelihood of a warmer, stormier winter in Northern Europe for example. So instead of the expected cold, dry winter over northern Europe, associated with an easterly QBO, it looks like we may see more storms, like those that brought flooding to the UK last winter.
“It’s not a sure thing,” Scott Osprey, climate scientist at the University of Oxford, told Science. “But it loads the dice towards those sorts of conditions.”
