There’s a change in the wind and it is so significant that it has caught the attention of NASA. The quasi-biennial oscillation, a pattern so regular you could practically set your watch to it, has suddenly changed. Scientists are now looking at recent wind anomalies they have observed to see if there has been an effect on the ozone layer and if there is whether or not it can affect human life.
Let me explain what all of this means.
The stratosphere is the layer of the earth’s atmosphere that sits immediately above the troposphere, which is the bit we live in. There is no weather as such in the stratosphere, there’s too little moisture there to fuel storms but it is home to several important and complex wind patterns. The air in the stratosphere slowly increases with altitude and therefore convection doesn’t occur and this makes it a relatively stable zone.
There is a repeating pattern of winds in the stratosphere called the quasi-biennial oscillation. As regular as clockwork, the same patterns are seen. These winds circulate in alternating easterly and westerly directions. It works like this:
When westerly winds developed at the tops of the stratosphere starts its gradual descent to the bottom, a layer of easterly winds replaced them at the top. On the other hand, westerly winds replace easterly winds in the top when it begins to descend. (source)
The cycle takes about 28 months before repeating itself. quasi-biennial oscillation. It’s regarded as the Old Faithful of the wind world, so regular and dependable is the cycle. (This book is kind of deep, but if you want to delve into historic weather patterns, you’ll love it.)
A change in the stratospheric wind patterns has been detected.
Towards the end of 2015, NASA scientists noticed that the pattern appeared to be reversing. The slowly defending westerlies stopped and reversed direction, moving upwards and therefore stopping the easterlies in their tracks. This was the case for a full six moths before the pattern reverted to normal in July this year.
The quasi-biennial oscillation has been observed continually for more than six decades and this is the first time these changes have been seen, and right now, we don’t know if it’s going to become a regular event.
So why does it matter?
Well, the reason the temperatures increase the higher you go in the stratosphere is due to ozone.
Solar energy is converted to kinetic energy when ozone molecules concentrated at 15-30 km absorb ultraviolet radiation, resulting in heating of the stratosphere. Due to the very low air density, even the small amount of ozone concentrated in the upper stratosphere is extremely effective in absorbing radiation, thus giving the ‘high’ temperatures at 50 km. (source)
Changes in the amount of ozone can have dire effects for those of us down here in the troposphere. The ‘hole’ in the ozone layer that was discovered in the 1970’s was said to be caused by man-made chemicals, notably CFC’s. They were banned in 1987 under the Montreal Protocol. Even so, scientists estimate it will take until 2070 for full repair of the ozone layer to occur. (source)
The ozone layer acts as a sieve, catching some of the UV radiation that reaches the surface of the planet. Without it, too much radiation would filter down and human health would suffer greatly with higher incidences of conditions such as melanoma (skin cancer) and cataracts.
The temperature in the stratosphere is crucial to maintaining the protection the ozone layer affords us. If the stratosphere cools the ozone layer is depleted and vice versa. Ironically as the troposphere warms, the stratosphere cools, and this is why scientists need to find out what’s going on with the temperatures and wind patterns that exist miles above our heads.
At this point, NASA has no idea at this point if the change in the quasi-biennial oscillation is going to be a regular thing caused by the contentious issue of climate change, if it was caused by a particularly strong El Nino, or if something else is behind it.
Are there any meteorologists, amateur or otherwise, who want to chime in?
(Hat tip to BW)