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Dennis

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    Stratosphere Temperature Watch 2015/2016

    in Spring Weather Discussion

    Posted · Edited by Dennis

    3 hours ago, BrickFielder said:

     Stratosphere forecasting is probably just as complicated as traditional weather forecasting and when you break things down there are both positive and negative factors which will affect whether a stratospheric warming will occur. Before I get into these factors lets just recap a few basics about stratospheric warmings.

    Warmings tend to come in three flavours. The first is a minor warming  (wave 1) which tends to push the stratospheric vortex away from the pole and tend to be common. These warmings can often push the vortex towards the UK resulting in wet and windy weather while setting up blocked weather patterns elsewhere. This blocked pattern can often provide the conditions for a major warming to follow in two to three weeks time. A major warming (wave 2) will tend to split the vortex in two and tends to be a little less common than minor warmings. The result for the UK depends on where the two lobes of the vortex are at a particular point, but often you can expect a slowly moving blocked pattern giving a cold spell for the UK. Finally there is the final warming which indicates the break up of the stratospheric vortex and ultimately the polar vortex which can lead to a variable pattern and some cold out breaks over the UK.

    These warmings are caused by upward propagating planetary waves  (Rossby Waves). OK so let me explain what I think these planetary waves are and how they work. Wave 1 represents a blocking  pattern where there is a single major blocking high pressure in northern latitudes. Typically this blocking high is connected to the Siberian High or norther European high pressure in Winter. Wave 2 represents a blocking pattern where there are two major blocking high pressure areas in northern latitudes. Typically these might be North western Canada  and Siberia. Wave 3 would represent three blocking highs in northern latitudes. Placement of the blocking high also seems to play a key role with a suggestion that  Blocking Highs  over  the  Euro-Atlantic  sector  tend  to  enhance  the  upward propagation  of  Planetary waves,  whereas  blocking highs  over  the  western  Pacific  lead  to  a  strengthening  of  the  polar  vortex.


    OK if you want to know more and see how these work follow the link below.

    http://www.sparc-climate.org/fileadmin/customer/5_Meetings/GA5_PDF/KazuakiNishii_SPARC_GeneralAssembly2014_14Jan.pdf

    So any old high pressure in winter will cause a stratospheric warming? No it is never quite that simple and there are precursor and conditions for these waves to propagate upwards into the stratosphere and affect the polar vortex. One source of precursors is possibly gravity waves in key areas with these smaller scale waves being able to penetrate above the stratosphere (mesosphere and ionosphere) to affect conditions there which will slow the winds slightly at the top levels of the stratosphere. These lowered winds then become susceptable to planetary waves disturbing them.

    Another link which sort of skirts around this.

    http://www.sparc-climate.org/fileadmin/customer/5_Meetings/GA5_PDF/PosterSessionB.pdf

    Now your head is probably totally confused about different waves I have better give a brief explanation of what gravity waves are as opposed to planetary waves. Gravity waves tend to result from either thunderstorms or low pressure systems crossing over mountain ranges. It turns out that particular mountain ranges and storms systems tend to have a large effect on whether planetary waves affect the stratospheric vortex. These gravity wave hot spots in the northern hemisphere winter include the mountains of Norway, Greenland and the UK. This might suggest that wet and windy weather in the UK and Norway might be a precursor to a stratospheric warming.

    Another link with some nice maps of where gravity wave hot spots occur.

    http://onlinelibrary.wiley.com/doi/10.1029/2012JD018658/full

    So we are starting to get a bit of a picture about how stratospheric warmings might come about. I have of course missed out on Kelvin Waves (particularly relevant to Tibetan plateau in winter) and solar tides. I am sure somebody here will go away and check up on these things to give an even clearer picture.

    Link explaining how all the different wave types combine together.

    http://arxiv.org/pdf/1412.0077.pdf

    Waves are part of the story but there is perhaps one more dimension that needs exploring a little and this is around ozone amounts over the pole. Ozone concentrations over the pole at high levels in the stratosphere alter the temperatures at those levels. Ozone depletion at the top of the stratosphere results in warming at this level and cooling through lower layers in the stratosphere. When temperatures go below -78 C Polar Stratospheric Clouds form which deplete the ozone further. This causes increased wind speeds in the stratospheric vortex which become ever harder to displace  (i.e. No amount of planetary waves could shift it). One cause of ozone depletion in the top layer of the stratosphere is the pulling down of Nox from layers above due to Energetic Particles. What I think this means is that space weather or more particularly solar activity can play a part in whether   stratospheric warmings occur (Note that EPP activity while related to the solar cycle can be slightly different).  Gravity waves can off course play a part in excitation of the thermosphere and mesosphere changing ozone concentrations as well.

    A little bit of discussion about this at the following link.

    http://www.atmos-chem-phys-discuss.net/15/33283/2015/acpd-15-33283-2015.pdf

    Seems to me that Geomagnetic activity might play a part as well.

    http://www.swpc.noaa.gov/products/notifications-timeline


    So having said all that and knowing a little about the drivers are we any closer to understanding whether a stratospheric warming is likely this winter ? The answer I think is that there are some   possibilities as energy is transferred from the troposphere into the stratosphere, but that we have a very strong stratospheric vortex which is going to take some shifting. After the current wave which we should not expect to shift the vortex much there is another wave forecast for around the 5th of January. I don't expect much from that one either but it might set up the conditions ready for a      further wave. So I think we are looking at late January and into February as realistic windows of      opportunity. Much will depend on ozone depletion due to cold stratospheric temperatures against ozone transport from lower latitudes.


    Figure7ag.thumb.png.c53f44fce0c1eff5adbe

    Credits to AER - Pls use a link for the WAF plot : http://www.aer.com/science-research/climate-weather/arctic-oscillation

    Stratosphere Temperature Watch 2014/2015

    in Spring Weather Discussion

    Posted

    hi dennis - this is currently what is happening way above our heads. unfortunately, it doesnt seem to have any consequences for nw europe and the strat vortex will reform over the pole and drift towards n greenland.  (and as posted earlier, the berlin charts are corrupt today and showing some old data - probably from last year)

     

    NNE winds later when the situation around Greenland set more blocking 

    post-23140-0-87438200-1420377965_thumb.p

    Stratosphere Temperature Watch 2014/2015

    in Spring Weather Discussion

    Posted

    Yes, I did see the GFS 0z run shortly after it come out but just looked at the ECM now, looking at the 10mb profile I did expect the wave 2 charts to show an increase, the EP flux prediction looks just about as poleward as ive ever seen.

     

    fluxes.gif

     

     

    The problem is that by now you would expect to see much more blocking in the extended ensembles.

    pls could u post a new chart ? Gr Dennis

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