What is a Sudden Stratospheric Warming (SSW)?

8 01 2013

You may have heard talk of the UK possibly seeing some colder weather next week and that ‘things going on’ in the upper atmosphere may be playing a part.

The ‘thing’ happening in the atmosphere is known as Sudden Stratospheric Warming (SSW). When it does happen, it attracts a lot of interest in the UK because it is sometimes linked to the onset of cold weather in winter.

Here we shed a little bit more light on the phenomenon.

What is an SSW?

The term SSW refers to what we observe – rapid warming (up to about 50 ­°C in just a couple of days) in the stratosphere, between 10 km and 50 km up.

You may have heard of the jet stream which helps to steer Atlantic weather systems towards the UK. Well there are other jet streams high up in our atmosphere in both the northern and southern hemisphere which circumnavigate the Earth from west to east. One of these, the Polar Night Jet, circles the Arctic.

Sometimes the usual westerly flow can be disrupted by natural weather patterns or disturbances in the lower part of the atmosphere, such as a large area of high pressure in the northern hemisphere. This causes the Polar Jet to wobble and these wobbles, or waves, break just like waves on the beach. When they break they can be strong enough to weaken or even reverse the westerly winds and swing them to easterlies. As this happens, air in the stratosphere starts to collapse in to the polar cap and compress. As it compresses it warms, hence the stratospheric warming.

How does it move down through the atmosphere?

As it turns out, waves can only move around the Earth’s atmosphere in westerly winds. Fluctuations in our weather send waves up through the atmosphere to the easterly winds in the stratosphere, where they travel no further, and instead break and reinforce the easterly winds, bringing the easterlies lower. This pattern continues until the easterlies have moved down to the troposphere – the lowest part of the atmosphere where our weather is.

It can take anything from a few days to a few weeks for this process to take place.

What impact does this have on the UK?

We normally expect our weather to come in from the west – with a flow of relatively mild air coming in off the Atlantic.

When an SSW brings easterly winds this tends to alter our weather patterns slightly, weakening areas of low pressure and moving our jet stream further south. This leads to high pressure over the North Atlantic, ‘blocking’ that flow of mild Atlantic air and dragging in cold air from the continent to the east. Exactly how cold it might be depends on the details of where the air comes from.

SSWs don’t always result in this outcome – but a cold snap follows more often than not, so the SSW greatly increases the risk of wintry weather.

Can we predict these events in advance?

Currently we can reliably predict individual SSWs about a week in advance, and we can detect them early on with satellite and other observations. This means we have some time to see how they develop and may impact our future weather.

The Met Office will continue to monitor the current event and, as ever, will keep everyone up to date on any periods of cold weather through our forecasts and warnings.


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15 responses

8 01 2013
Goaty's News

Reblogged this on Goaty's News.

12 01 2013
nuwurld

This is a little like playing ‘join the dots’. I’ll endeavour to say what Adam really wanted to say, in my opinion!

Adam has studied and written about the effects of solar variability on the Northern Hemisphere. Indeed his work has been published in Nature Geoscience. Please check this link.

http://www.metoffice.gov.uk/research/news/solar-variability

In this Met Office web page he describes the same effect with connection to declining solar UV radiation. Strangely above he does not mention solar variability!

To further fill in the gaps, this report was written about a then current affect that had produced a measured SSW, with Easterlies due within days.

Now for the point of my writing. For the past nine months of this weak solar cycle 24 maximum the Sun has been pulsing bursts of UV at 27 day intervals. However, from the 23rd of November 2012 until 4th Jan she fell silent with a spot count daily average around 30. That’s about 1/5th of what normal peak Sun would be.

Through the 5th Jan 2013 through to the 8th, the date of this report the Sun burst into life again.

Adam and his colleagues must be jumping for joy because not only have they measured the SSW itself, the Easterlies came and they occurred because of the upper atmosphere collapse due to weakened solar UV radiation!

Why is the Met Office so fearful of suggesting that the Sun can and does directly influence weather and climate through its variability?

13 01 2014
sabretruthtiger

Of course he doesn’t mention the key factor -Solar cycles. He would lose his job as they’re all run by the global warming alarmist establishment.
They must claim it’s purely atmospheric heat differential then try to link it to CO2.

19 01 2013
nuwurld

As a UK citizen, I am proud of my UK Met Office. I want to remain so. NASA is currently freeing itself and shaking off the shackles of Jim Hansen an his ‘untouchable’ regime. The Met Office has recently, and without public notice adjusted and reduced it’s prediction with respect to future global warming. Your public statement is a scientific nonsense. That is not the way science is done. At some time you will remove that statement.

Please Met Office, with knowledge that Adam Scaife has studied historical SSW’s, would you please comment on the above (acknowledge or deny), and please ask Adam, who is in appraisal not rebuke to comment on the relative magnitude of this SSW. As far as I am aware an SSW disturbance of the polar vortex and it’s associated pressure systems can take between 1 week to 2 months to reform. As meteorologists your prediction is not set in stone. It is just that. A prediction, based on the best knowledge at that time, something you do every day. What is the relative magnitude of this event?

On a blog I would expect the person monitoring comments to be in some way able to respond, thankyou.

19 01 2013
Dave Britton

It is great to hear that you are rightly proud of the Met Office. Thank you.
In relation to your question – are you inferring that an SSW is linked our latest decades forecast to 2017? It is not correct to link an individual SSW event, which can effect weather on a regional scale for a few weeks, with a forecast for global temperatures over the next five years. The big driver of global average temperatures is ocean temperatures and I would refer you to an article written by our chief scientist which explains these forecasts in more detail at http://www.metoffice.gov.uk/research/news/decadal-forecasting.
If I have misunderstood your question then accept my apologies and let me know.

21 01 2013
nuwurld

Hi David, sorry I had to provoke a response. Strange how my question about the SSW remained unanswered for a week but as soon as I mentioned global events a reply was ready. My response to yours will be broken down and labelled. If you think that the two issues are not connected then please go back to your chief scientist. The thing is about science and mathematics is that the basic principles are set in stone. If you ‘understand’ you won’t have to refer me to a ‘chief scientist’. Any questions I have to ask about something that is prompted by the Met Office I would expect you sir, to be able, and willing to answer. If you don’t know the answer then three options prevail. Either you take it upon yourself to find out for myself and other readers, or you provide a link where I can find something other than a generic response or you dismiss my discussion by ignoring it. Which, inadvertently, says a lot more than you think. So David, are you with me?

22 01 2013
Dave Britton

I am in the process of pulling together the answers to your questions and we will respond in due course. Thanks.

21 01 2013
nuwurld

David in order sir,
1) Does the Met Office correlate a SSW with any solar activity change?

2)With acceptance that from the 90’s many years passed without significant Easterlies,’ ‘what has changed in recent years?’

3)Whilst the temperatures where rising for whatever reason, wasn’t it true that the jet stream was trending north?Now with the onset of ‘proper winters’ the jet stream is trending south. Isn’t this now a cooling signal.

4) Are you aware that current solar activity is low and all predictions say that will continue for decades?

5) Does the Met Office accept or deny that all the upper atmosphere kinetics are through solar ionising radiation. That is potentially, the solar investment in upper atmosphere is stored energy. That is stored gravitational potential energy. Which during slight durations in solar flux variations, the upper atmospheric collapse will transfer energy to lower levels, as in a SSW. But during longer periods of solar reduction the whole atmosphere will have to adjust to restore equilibrium.

22 01 2013
Dave Britton

1) Does the Met Office correlate a SSW with any solar activity change?
It is not possible to ‘correlate’ a single SSW event with solar activity but there is evidence that solar activity can alter stratospheric winds which are intimately related to sudden stratospheric warmings.

2) With acceptance that from the 90′s many years passed without significant Easterlies,’ ‘what has changed in recent years?’
This is an ongoing area or active research and the scientific community does not have a full explanation of this. Of course internal variability could certainly be one possibility here and would certainly deliver such changes as we have found in previous studies (see Butchart et al 2000: Response of the stratospheric climate to projected changes in the concentrations of well mixed greenhouse-gases from 1992 to 2051.J. Climate, 13, 2142-2159.)

3) Whilst the temperatures where rising for whatever reason, wasn’t it true that the jet stream was trending north? Now with the onset of ‘proper winters’ the jet stream is trending south. Isn’t this now a cooling signal?
Global temperature records remain at record high levels and a forecast to remain around record warm levels. see http://www.metoffice.gov.uk/news/releases/archive/2012/global-temperatures-2012

4) Are you aware that current solar activity is low and all predictions say that will continue for decades?
The Sun is more active now than it has been since 2009. On longer timescales, the current solar maximum is indeed muted and predicted to be lower than recent maxima. Some solar physicists are suggesting the onset of a new long term minimum and we are indeed aware of this and have been working on the implications – see for example Jones et al 20?? but at present can’t explain year-to-year variations in UK winter weather.

5) Does the Met Office accept or deny that all the upper atmosphere kinetics are through solar ionising radiation. That is potentially, the solar investment in upper atmosphere is stored energy. That is stored gravitational potential energy. Which during slight durations in solar flux variations, the upper atmospheric collapse will transfer energy to lower levels, as in a SSW. But during longer periods of solar reduction the whole atmosphere will have to adjust to restore equilibrium?
The idea that all solar effects on the atmosphere are due to ionising radiation is not consistent with current peer reviewed science onf solar effects on climate. Mechanisms for any solar effects on climate are outlined for example in the peer reviewed work by Ineson et al 2011 (Solar forcing of winter climate variability in the Northern Hemisphere, Nature Geoscience 4,753–757(2011) doi:10.1038/ngeo1282)

22 01 2013
nuwurld

David, thank you for taking the time to answer each and individual question. Also for doing so in a measured response. I apologise for sounding abrupt earlier. If I may, I will respond to each in turn, before asking further questions. Thanks again.

23 01 2013
Dave Britton

No worries. Thanks

24 01 2013
nuwurld

David, I am sure you where expecting some kind of response. It’s going to be a bit heavy I’m afraid.

David, the title of this Met Office news requires some qualification. The question is asked, ‘What is a Sudden Stratospheric Warming?’.

But is it answered?

That depends on how little the reader wants to know, or how little the describer wants to convey. I pick up on words and phrases like ‘thing’, ‘tickle the top of the troposphere’,

No. I’ve just stopped myself there, looking for odd words and phrases that don’t add up. The whole lot DOES NOT MAKE SENSE.

A Sudden Stratospheric Warming, at least a major one, like this, is the SINGLE, MOST DRAMATIC EVENT IN THE ATMOSPHERE.

Do you see the difference between my description and yours.

What your description lacks is a believable mechanism that explains a displacement of all related weather systems over an area of hundreds of millions of square miles, throughout a median polar area.

That’s a lot of energy.

The polar jet stream is displaced because the ‘Siberian High’ and the ‘Canadian High’ strengthen and move and block the jet stream. It is these ‘anti cyclones’ that bring the ‘easterlies’.

That requires a stupendous amount of energy. The source of that energy and its sudden arrival is the question to be answered. Along with a logical, physical approach.

NASA has deployed not one, but many successive satellites to constantly check and re-check solar ultraviolet levels and variability. Why would they do that? Why would they bother to measure repeatedly something that never reaches the ground?

Well, because of implications. Whilst the atmosphere protects us from ALL the UVC and very nearly all of the UVB, there is a consequence. The natural oxygen, ozone, oxygen cycle invests solar UV energy in the upper atmosphere kinetics. The UV ENERGY IS ABSORBED BY THE ATMOSPHERE. It literally drives the upper troposphere into all the upper layers extending beyond 500km above the surface. That equates to a massive investment in gravitational potential energy.

We’ve all heard the expression, ‘What goes up, must come down’. And when it does, it becomes kinetic. That’s thermal in a gas. And that’s conservation of energy!
Without the higher photon energy beyond visible light the atmosphere would be of a much smaller volume, and hold much less energy.

So active sun, with greater UV and soft X-rays ‘inflates’ the upper atmosphere. But here is the trick. The energy is largely stored, for the simple reason, the one that greenhouse gas aficionados cannot appreciate, atmospheric energy storage is in the form of its thermal energy, its gravitational potential energy and the FACT THAT IT RADIATES VERY LITTLE AT ALL. Therefore nearly all the solar UV becomes an inevitable part of Earth’s energy budget. BY DIRECTLY HEATING THE ATMOSPHERE.

When the Sun reduces the UV, the inflation of the upper atmosphere starts to collapse and destabilise.

Over the poles during their respective quiet winter nights, a coriolis vortex forms of massive proportions. A massive low pressure forming the central portion of the polar convective cell.

Destabilised upper Mesosphere and Thermosphere falls into the low pressure of the polar vortex due to solar reduction.

In doing so a massive amount of gravitational energy and CONSERVED MOMENTUM is dumped unceremoniously on top of and into the polar vortex.

The pressure integration and temperature increase stabilises when the system can support the weight of material above. (Thermodynamics, I feel we’ll end up at this one later!)

The net flow, thermal distribution and resultant pressure changes propagate through the entire system until achieves a point of stability. At which point the only forces present are those required, thermodynamically to restore the adiabatic to the environmental profile in equilibrium with the current solar flux, and the inevitable conserved momentum.

The resultant easterlies over certain areas are due to the strengthening and displacement of the Siberian an Canadian highs.

Food for thought.

25 01 2013
Dave Britton

Thanks, The energy does not come directly from the changing UV but fromt he shift ion the tropospheric jet itself, which contains plenty of energy of its own.

I have suggested a couple of papers which may answer your question more fully:

• Thompson, D. W. J., and T. Birner, 2012: On the linkages between the tropospheric isentropic slope and eddy fluxes of heat during Northern Hemisphere winter. J. Atmos. Sci., 69, 1811-1823.
• Kodera, K. And Kuroda, Y, 2000: Tropospheric and stratospheric aspects of the Arctic oscillation. Geophysical Research Letters, 27, 3349 – 3352

31 01 2013
nuwurld

Before going into any details about the details of thermodynamic equilibrium, it appears that the stratosphere never recovered from the last warming, and that the second, major, or possible final warming of the winter is underway.

Any comments David?

Are we ready for the second bought of winter?

31 01 2013
Dave Britton

Looking at the UK Outlook, thought the first half on February it is tending to turn colder and rather unsettled across the UK. We are likely to see a mixture of sunny spells and blustery showers, which will turn increasingly wintry, though probably falling as rain or sleet in the south at first. There is the potential for some accumulations of snow in places exposed to the north and northwest.

Through the remainder of the month there are large uncertainties at this forecast range, however indications are that colder than average conditions may continue across most parts of the UK.

You can find out more and stay right up to date at http://www.metoffice.gov.uk/public/weather/forecast/#?tab=regionalForecast on the Met Office website.

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