Stratosphere Cooling and Warming

[chionomaniac]

After reading many of GP posts I have gathered that a cold polar stratosphere is not good for our own long term cold prospects. Why is that? And what are the mechanisns involved when the stratophere warms to transfer the cold?

Thanks in anticipation.

c

Ps any help in explaining the stratosphere and stratosphere anomoly charts would also be appreciated!

[BrickFielder]

First of a couple of charts to compare one from the end of 2007 and the other from 2006.

These charts show temperature anomalies and you can clearly see warm periods in January of 2006 where there have been none towards the end of 2007.

Charts available here

Notice how the warming during january moves down to below 100hPa at the start of February 2006. This changes the pattern of weather and gave the UK a cold snowy period.

The first question to be asked must surely be where do these warmings come from. The answer is that they have their orrigins in unsually strong weather events at the surface. Typically what happens is the warming is caused by friction of winds at different levels(as the wind is slowed or speeded up). As air at low levels blows in the opposite direction to that in the stratosphere it slows the winds down. That slowing passes all the way up to the top of the stratosphere before working tis way back down. Obviously the background wind direction in the straosphere plays a part (QBO) as to whether low level winds are able to affect stratospheric winds.

The stratospheric warming site

Sparc (Stratospheric Processes)

Mark Baldwin's site

Decadal variabilty of the stratosphere

Stratospheric forecasts as well as being available at the CPC site are available

Here

and polar vortex forecasts here

The most important thing to remember is that the stratosphere is an important driver of the artic oscillation (Sea Surface Temperatures and snow and ice coverage to name but two other factors also play a part) as can be seen from the following chart.

Another way of thinking about it is to think of a big low pressure vortex in the stratosphere which at times can be shifted or disturbed. Beneath the low pressure vortex pressure changes at the surface by nature of the tropopause (boudary being lifted or depressed) being changed.

Its a bit complicated but hopefully I have provided a starting point and maybe GP will come along in a bit with a more lucid explanation.

[chionomaniac]

Thanks Brickfielder,

I'm a bit busy at work but its something i've been wondering for a while so I will read and digest this evening

[chionomaniac]

Thanks once again brickfielder I have had a long read around the subject with the links you have provided.

I realise that to understand stratospheric warming/cooling I needed to fully understand how the QBO works.I have read up on this(http://en.wikipedia.org/wiki/Quasi-biennial_oscillation) and now feel that I can visualise how this oscillation pattern occurs now. Are the Rossby waves the waves flowing towards the poles from the QBO and are we in a westerly or easterly phase?

Looking at the latest Stratosphere temps fro this year

am I correct in reading that the stratosphere is cooler(marked by the greens) than average which may then have a bearing on the Arctic oscillation keeping us in a positive (less favourable?) phase.

Current AO Neutral -heading positive

Arctic oscillation good explaination - http://www.nsidc.org/arcticmet/patterns/ar...scillation.html

Also am I right in saying that when the stratosphere warms above the poles and this warming breaks through the tropopause into the troposphere then this warmth displaces the cold polar air into latitudes further south?

Please feel free to correct me if anything is wrong and if anyone else has anything else to add on the subject to help my understanding the please do so. I think I am getting there on a complex subject!

c

Other useful link I used

http://en.wikipedia.org/wiki/Sudden_stratospheric_warmings

Edited January 10, 2008 by chionomaniac

[johnholmes]

great idea this thread, I'm learning all the time, keep the entries and explanations coming.

[BrickFielder]

QBO is easterly or was last time I looked.

QBO Data

I think the QBO is the winds in the stratosphere above the tropics.

There are a number of different waves to consider in the atmosphere. The one you mention the rossby wave is largely based in the troposphere and relates to the undulations of the jetstream or the boundaries of the hadley and walker circulations.

Atmospheric Rossby waves

Planetary zonal waves (rossby waves I think) are the source of changes in the stratosphere and these are different to gravity waves. Essentially low pressure and high pressure at the surface causes ripples in the tropopause which cause ripples in the stratosphere which come back down to cause ripples in the tropopause which affects the weather. Think of the ripples causing the winds to slow down the winds going across them. These winds then slow down the winds above them and so on untill the top when slower winds at the top slow down the winds below. Each time you get differences in winds speed you get friction and warming. Another source of these ripples is weather systems crossing the great mountain ranges of the himalayas and the rocky mountains.

The greens on that chart do mean it is colder.

Yes the stratosphere can have a bearing on the artic oscillation (AO) which in our neck of the woods is the difference in pressure between iceland and the azores. A positive AO means a strong icelandic low pressure.

In a week or so the weather patterns will change across america changing the rossby wave pattern which I think will result in a warming (maybe) which will take about 3-4 weeks to work up and back down again.

More Reading

Edited January 11, 2008 by BrickFielder

[chionomaniac]

QBO is easterly or was last time I looked.

QBO Data

I think the QBO is the winds in the stratosphere above the tropics.

There are a number of different waves to consider in the atmosphere. The one you mention the rossby wave is largely based in the troposphere and relates to the undulations of the jetstream or the boundaries of the hadley and walker circulations.

Atmospheric Rossby waves

Planetary zonal waves (rossby waves I think) are the source of changes in the stratosphere and these are different to gravity waves. Essentially low pressure and high pressure at the surface causes ripples in the tropopause which cause ripples in the stratosphere which come back down to cause ripples in the tropopause which affects the weather. Think of the ripples causing the winds to slow down the winds going across them. These winds then slow down the winds above them and so on untill the top when slower winds at the top slow down the winds below. Each time you get differences in winds speed you get friction and warming. Another source of these ripples is weather systems crossing the great mountain ranges of the himalayas and the rocky mountains.

The greens on that chart do mean it is colder.

Yes the stratosphere can have a bearing on the artic oscillation (AO) which in our neck of the woods is the difference in pressure between iceland and the azores. A positive AO means a strong icelandic low pressure.

In a week or so the weather patterns will change across america changing the rossby wave pattern which I think will result in a warming (maybe) which will take about 3-4 weeks to work up and back down again.

More Reading

Thanks again -Its taken a few days to absorb the latest info!

Regarding Atmospheric Rossby waves in the troposphere - the chances of receiving cold weather are far greater if these waves are more numerous and with greater amplitude? If the jet is flat then there are fewer of these waves and we are more likely to get zonal type weather in this country - such as seen in MJO phases 3-5 when there is increased tropical convection.

Planetary zonal waves are different to atmospheric rossby waves as they are based in the stratosphere but can have an affect on the troposphere as you describe above.

I think its getting clearer in my head.

c

[chionomaniac]

I have another question on stratospheric warming(sorry to be persistant!).

It appears looking at the evidence that a significant minor stratospheric warming event is just concluding:

However it looks like this warming has not filtered down to the troposphere giving us any beneficial cold knock on effect. Is there any way of predicting which warming effects will benefit us for future reference?

It appears that the stratosphere is predicted to warm up again

Great.

But when looking at the long term averages of warming events in the stratosphere at 30hPa it appears that the last warming event even though it outwardly looked great, it hardly got above the long term average for warmth at that layer in the stratosphere!

So that leaves the question is the amount of warming achieved, or the amount of temp change in the stratosphere, more important for future cold troposphere effects ?

Many thanks in anticipation.

c