Wednesday, 21 September 2016

Disruption of QBO — One of Our Most Predictable Atmospheric Clocks

Giant Gravity Waves Smashed Key Atmospheric Clock During Winter of 2016 — Possible Climate Change Link



19 September, 2016

Two [climate change] effects [of Arctic warming] are identified … : 1) weakened zonal winds, and 2) increased [Rossby] wave amplitude. These effects are particularly evident in autumn and winter consistent with sea-ice loss… Slower progression of upper-level waves would cause associated weather patterns in mid-latitudes to be more persistent, which may lead to an increased probability of extreme weather events … — Evidence linking Arctic amplification to extreme weather in mid-latitudes, Dr. Jennifer Francis and Dr. Stephen Vavrus, Geophysical Research Letters (emphasis dded)

The recent disruption in the quasi-biennial oscillation was not predicted, not even one month ahead. — Dr. Scott Osprey

This unexpected disruption to the climate system switches the cycling of the quasi-biennial oscillation forever. — Professor Adam Scaife
scientists believe that the quasi-biennial oscillation could become more susceptible to similar disruptions as the climate warms. — Physics.org (emphasis added)
jet-stream-crossing-equator-on-february-18-of-2016

(During February of 2016, high-amplitude Jet Stream waves or gravity waves interfered with the upper-level Equatorial Winds. This disruption was so significant that it caused a seasonal upper-level wind pattern near the Equator to change direction, a shift that was unprecedented in modern observation. Note how the upper-level wind flow frequently intersects with and even appears to cross the Equator at some points. Image source: Earth Nullschool global 250 hPa capture for February 18, 2016.)

*****
I’ve said it before, and I’m going to say it again — loss of predictable seasons, or seasonality, due to human-forced climate change is very big deal. And regardless of how all the scientific details specifically pan out, there are now observed changes to Northern Hemisphere winter, possibly due to human-forced warming, that are apparently starting to undermine its traditional seasonal climate behaviors. As a result, weather patterns appear to be shifting toward greater extremes and lower levels of predictability.

QBO — One of Our Most Predictable Atmospheric Clocks…

For decades now, scientists have been observing a kind of atmospheric clock tick-tocking high above the Equator. Up in the stratosphere, 10 to 13 kilometers above the Earth, winds tend to flow either east to west or west to east. These air flows change direction about every 28 to 29 months. This feature, called the quasi-biennial oscillation or QBO, has never significantly varied. It has always flowed in one direction for a predictable period of time and then switched to flow in the other direction.

Winds flowing at this level of the atmosphere over the Equator have a far-reaching effect,particularly on the winter climate of northern Europe. There, westerly high-level Equatorial winds are known to bring warmer, wetter winters. Easterlies in the stratosphere over the Equator are known to bring cooler, drier winters. The key to remember is that the QBO has always been both amazingly predictable itself, and had equally predictable climate effects. As a result, meteorological observation of the QBO natural-variability pattern enabled forecasters to get an idea of what weather trend to expect for winter — not just during a single year, but also over a longer time horizon.

and Climate Change May Now Be in the Process of Breaking It

What happens if the QBO becomes less predictable due to influences such as human-forced polar warming? What happens if the big meanders in the Jet Stream produced by this warming dig down all the way to the Equator during Northern Hemisphere winters and start to shove at the upper-level Equatorial wind field, causing the QBO to switch? If that happens, then a major aspect of Northern Hemisphere winter seasonal variability will have been fundamentally altered by climate change. Winter would become less like it is now and more like some strange, difficult-to-predict, climate-change-morphed hybrid of a thing.
Over the past decade, scientists like Dr. Jennifer Francis have observed strange changes to the Northern Hemisphere Jet Stream. In winter, the North Pole has tended to exhibit extreme relative warming versus the rest of the Northern Hemisphere. This warming has created less difference in temperature from north to south during this season. As a result, it appears that the Jet Stream has slowed and is generating very large atmospheric waves, known as gravity waves or Rossby waves. At times, these waves have linked upper-level air flows between the Tropics and the North Pole.



(For years now, Dr. Jennifer Francis has warned that polar amplification could lead to some weird and extreme weather, especially during winter. However, no one initially predicted that the large Jet Stream waves apparently resulting from polar warming would completely disrupt the upper-level Equatorial winds as appears to have happened last February.)

Such strong polar warming during winter is called polar amplification, an effect produced by climate change. Polar amplification happens because greenhouse gasses resulting from fossil-fuel burning (like carbon dioxide and methane) preferentially trap heat during times of darkness. During December through March, large sections of the North Pole are blanketed in the dim of Polar Night. 

During this time the heat-trapping effects of these gasses really go to work. Additionally, heat from the ocean is transferred through the thinning veil of sea ice over the Arctic Ocean even as local carbon stores add to the overburden of the heat-trapping gasses already in place. The net effect is a much warmer-than-normal Arctic during winter. This warming appears to be doing a serious number on the Jet Stream and, apparently, even Equatorial atmospheric circulation.
Unprecedented QBO Switch in February 2016

During the most recent winter, scientists observed these high-amplitude Jet Stream waves reaching all the way into the Equatorial upper-level wind field with enough oomph to switch an east-west wind pattern to west-east. This switch was entirely unpredicted and unprecedented. No one expected it and it has never before been observed.

The weather pattern for a big swath of Europe was, as a result, flipped from the expected cool and dry to warm and wet. If you had told any atmospheric scientist that such a set of changes would happen, they might have categorically dismissed these claims. But now, some scientists are starting to look at the possibility that the recent QBO flip was due to a climate warming-related influence.

geographical-pattern-of-surface-warming
(Geographic pattern of surface warming as provided by the IPCC. Uneven relative warming of the surface of the Earth may result in some unexpected changes to larger atmospheric circulation patterns. Scientists now indicate that future flips in Equatorial wind patterns,like the big switch that occurred this past winter, may be driven by such atmospheric warming. Image source: IPCC.)

There is a possibility that the recent flip was related to large atmospheric waves which are potentially a result of polar amplification. These waves appear to have impacted the upper-level Equatorial winds, and so are not necessarily related to natural climate variability.
To initiate such a big atmospheric change requires a great deal of force. The equatorial wind field and atmospheric mass is generally the heaviest, is typically the region with the greatest atmospheric inertia. Having an outside influence, like polar warming and associated gravity waves, generating a flip in its flow is about the meteorological equivalent to rivers running up hill. Apparently, due to climate change, atmospheric ‘rivers’ in the Jet Stream may now be capable of doing just that, and that’s pretty disturbing.
Links/Statements/Hat tips:

Scientific hat tip to Dr. Jennifer Francis
Scientific hat tip to Dr. Scott Osprey
Scientific hat tip to Professor Adam Scaife


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