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2014/15 forecast

Mark Bayley


[color=rgb(40,40,40)][font='Open Sans'][size=3][center][b]2014/15 Winter Forecast [/b][/center][/size][/font][/color]

[color=rgb(40,40,40)][font='Open Sans'][size=3][center]My attempt at a winter forecast. Some of the theory is taken from a previous project i undertook at University. I have attached references that i have used/think may be of interest. Apologies if it does not flow well. Apparently i am dyslexic although i've read over it a few times and i think its devoid of mistakes![/center][/size][/font][/color]
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[b]Factors considered[/b][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
[font=symbol]· [/font]QBO[/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
[font=symbol]· [/font]October snow cover[/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
[font=symbol]· [/font]Autumn sea ice extent[/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
[font=symbol]· [/font]ENSO[/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
[font=symbol]· [/font]Solar output[/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
[font=symbol]· [/font]Long range models[/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
[font=symbol]· [/font]OPI (briefly)[/size][/font][/color]

[color=rgb(40,40,40)][font='Open Sans'][size=3][center][b]QBO[/b][/center][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
The quasi-biennial oscillation (QBO) is a quasiperiodic fluctuation of the equatorial zonal wind in the tropical stratosphere between the westerlies and easterlies. In westerly phase stratospheric warming events during winter occur less frequently. Last winter theQBO was in westerly phase, contrasting to this winter, where it is in easterly phase. Stratospheric warming events are more common in this phase. I’ll not bog down with the physics and processes, so will leave it at this. The current phase of the QBOfavours a colder than average winter. See further information if you wish to read more on the QBO. [/size][/font][/color]
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[url="http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/qbo/"]Current/past phases of the QBO (note shaded area equates to westerly winds)[/url][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]

[color=rgb(40,40,40)][font='Open Sans'][size=3][center][b]October Snow cover[/b][/center][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
October Eurasian snow cover anomalies have been correlated with the wintertime AO (see Cohen et.al., 2011 at the end). Cold and dense air associated with snow cover promotes high-pressure formation, whereas warmer buoyant air over ice-free landmass promotes lower pressure formation. More expansive and stronger Siberian high-pressure systems are therefore favoured during years of greater autumn snow cover. Cohen and Entekhabi, (1999) first proposed a strengthened Siberian high leads to increased atmospheric wave breaking into the stratosphere. Such events can in turn lead to a phenomenon known as sudden stratospheric warming. Preceding sudden stratospheric warming events atmospheric waves propagating into the stratosphere decelerate upper westerly zonal winds (e.g. Martius et al., 2009). During strong atmospheric wave breaking events, found to be associated with a stronger and more expansive Siberian high, mean zonal winds may reverse (become easterly) and thereafter sudden stratospheric warming occur (Martius et al., 2009). This prevents further atmospheric wave breaking penetrating into the stratosphere, causing downward propagation of stratospheric easterly winds and warming into the underlying troposphere. Zonal wind reversal in the troposphere leads to disruption of the polar vortex and formation of positive height anomalies (-AO). Colder air is thereafter displaced into the mid-latitudes by -AO[/size][/font][/color]
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The recent Eurasian October snow cover extent was amongst the highest on record. I reconstructed 1000mb Geopotential heights for the lowest/highest October snow cover years. For the highest snow cover years I narrowed down to those months that occur within the easterly phase of the QBO (n at end of section). [size=4]A strong signal for positive height anomalies across Greenland is present during high snow cover years that occur in the easterly phase for the QBO (+SC/easterly QBO). In contrast a strong signal for lower than normal heights is present for years that occur during low snow cover years and the westerly phase of the QBO (-SC/westerly QBO). A greater southerly track of the jet stream is also found.[/size][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
[size=4]Left: [/size]-SC/easterly QBO Right : [size=3]+SC/westerlyQBO[/size][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
[url="https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-92671400-1416177202.png"][img]https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-92671400-1416177202_thumb.png[/img][/url] [url="https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-45118800-1416177203.png"][img]https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-45118800-1416177203_thumb.png[/img][/url][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
[size=4]Left: [/size]-SC/[size=3]easterly[/size] QBO Right : [size=3]+SC/westerlyQBO[/size][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
[url="https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-90194500-1416177205.png"][img]https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-90194500-1416177205_thumb.png[/img][/url] [url="https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-42269200-1416177206.png"][img]https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-42269200-1416177206_thumb.png[/img][/url][/size][/font][/color]
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An stronger signal for positive height anomalies occurs in January during +SC/easterly QBO years. In contrast, lower than normal heights (i.e. +AO) occurs during -SC/westerly QBO. The mean jet stream position during +SC/eastly QBO years is south of the UK, which contrasts to -SC/westerly QBO years, where it is across the UK (i.e. a wet and often mild winter results!)[/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
[size=4]Left: [/size]-SC/[size=3]easterly[/size] QBO Right : [size=3]+SC/westerlyQBO[/size][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
[url="https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-89726700-1416177204.png"][img]https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-89726700-1416177204_thumb.png[/img][/url] [url="https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-41892000-1416177205.png"][img]https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-41892000-1416177205_thumb.png[/img][/url][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
[size=4]Left: [/size]-SC/[size=3]easterly[/size] QBO Right : [size=3]+SC/westerlyQBO[/size][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
[url="https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-90012200-1416177206.png"][img]https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-90012200-1416177206_thumb.png[/img][/url] [url="https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-40162000-1416177207.png"][img]https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-40162000-1416177207_thumb.png[/img][/url][/size][/font][/color]
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Similarly a strong signal for positive height anomalies during +SC/easterly QBO years is found in February. In contrast, lower than normal heights (i.e. +AO) occurs during low snow cover/westerly QBO years. I forgot to reconstruct mean jet stream position, however it is clear that during +SC/easterly QBO years that the jet stream is to the south of the UK based upon the 1000mb geopotential height anomalies.[/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
[size=4]Left: [/size]-SC/[size=3]easterly[/size] QBO Right : [size=3]+SC/westerlyQBO[/size][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
[url="https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-91645300-1416177203.png"][img]https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-91645300-1416177203_thumb.png[/img][/url] [url="https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-40788300-1416177204.png"][img]https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-6181-0-40788300-1416177204_thumb.png[/img][/url][/size][/font][/color]
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The mean index value for the AO during +SC/eastly QBO years is; -1.01 December (n12); -0.97 January (n12); -1.44 February (n10). No strong signal for the NAO exists (albeit a weak negative signal for December and February); -0.31 December; 0 January; -0.33 February.[/size][/font][/color]
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In summary a clear signal for -AO during winters that occur in +SC/easterly QBO years is present. However, there is no strong temperature signal for the UK (also note a weaker forcing on the NAO). Despite that, -AO will support greater periods of prolonged cold across the UK, should the segments of the PV fall into the right position (which is most important, and crucial to recognise despite great AO forcing, stratospheric warming evetns DO NOT automatically result in UK cold). To conclude; this year’s snow cover, accompanied by the phase of the QBO, is supportive of atmospheric conditions (i.e. -AO) conducive to a colder than average winter.[/size][/font][/color]

[color=rgb(40,40,40)][font='Open Sans'][size=3][center][b]Autumn sea ice conditions[/b][/center][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
During low sea ice years higher geopotential heights over the Arctic occurs (see Jaisor et.al., 2012). This is attributed to an increase in the temperature of the lower troposphere (via an increased transfer of heat from the open ocean). Warmer air is less dense and therefore forms an area of increased geopotential thickness. Greater geopotential heights oppose the normal polar vortex Arctic westerlies, and instead favour meridional flow, supporting -AO (note other feedbacks exist; see attached literature). Others (e.g. Liu et al., 2012) have noted that a decrease in Arctic sea ice is associated with an increased occurrence of winter high-pressure blocking systems in the high latitudes, most particular in Eastern Europe, Siberia, Alaska and the North West United states. Recent studies have noted that sea ice anomalies around the Kara and Laptev sea have a strong forcing on the AO (e.g. [size=3]Baek-Min et.al., 2014[/size][size=4]). This year sea ice extent was negative, however not as low as years previous. Sea ice extent was also higher in the aforementioned regions, thus it may be expected that this year’s sea ice anomalies potential to force -AO may be less strong than previous winters. Despite this sea ice extent is still at record lows, and based on other climatic feedbacks, I’d suggest is still supportive of a colder than average winter.[/size][/size][/font][/color]
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[url="http://nsidc.org/arcticseaicenews/"]October sea ice extent[/url][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
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[size=4]Seasonal anomalies in 1000-500 hPa thicknesses (m) north of 40 N for 2000–2010 (years of low sea ice) relative to 1970–1999 (years of high sea ice): a) autumn; b) winter. White crosses indicate statistical significance. Reproduced from Franics and Varvus, (2012). Lower sea ice correlates strongly with increased [/size]occurrence[size=4] of winter [/size]blocking[size=4] systems[/size][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]

[color=rgb(40,40,40)][font='Open Sans'][size=3][center][b]ENSO[/b][/center][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
Recent work has shown that ENSO, when close to neutral, has a minimal impact on the northern hemisphere mid-latitude weather patterns. Some such as Cohen suggest that ENSO, unless strong, is relatively useless in winter forecasting. Weak to moderate El Ninos have however been correlated with colder than average winters across NW Europe (although not strongly). At present El Nino is weak, and is not predicted to gain significant strength during winter . The current ENSO pattern therefore favours a colder than average winter. Unfortunately I am unable to cover ENSO in the depth [size=3]of [/size][size=3]snow [/size][size=3]cover [/size][size=4]and [/size][size=3]sea ice[/size][size=4], mainly as the charts posted are being used as part of my research project.[/size][/size][/font][/color]
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[url="http://www.cpc.ncep.noaa.gov/products/predictions/90day/tools/briefing/sstaa.gif"]E[/url]NSO long range prediction[/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]

[color=rgb(40,40,40)][font='Open Sans'][size=3][center][b]Solar output[/b][/center][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
Increased solar output favours milder than average winters. Currently solar activity has picked up, although is not notably strong. No strong winter signal is favoured from current solar activity.[/size][/font][/color]
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[url="http://www.climate4you.com/Sun.htm"]Current sun spot activity[/url]. Note the increase since 2010[/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]

[color=rgb(40,40,40)][font='Open Sans'][size=3][center][b]Long-range climate models[/b][/center][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
A number of long range forecast models are/where predicting a milder than average winter (e.g. CFS). Long range forecast models may not take into account snow and sea ice feedbacks. Often, long-range forecast models turn out to be wrong (e.g. CFS). Although not discounted, little emphasis is placed on these models. To summarise, the output from long range climate models favours a milder than average winter.[/size][/font][/color]

[color=rgb(40,40,40)][font='Open Sans'][size=3][center][b]OPI[/b][/center][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
Not really got time to cover this so I refer everyone to OPI thread where there has been some excellent analysis by the likes of Steve Murr and others. A relationship between the OPI and AO has been noted, with correlations as strong as 0.9. Further to this a good relationship between the OPI and CET is noted (-OPI correlates with below uk temps). The final OPI figure was amongst the most negative of those recorded. This would add further support to atmospheric conditions (i.e. -AO) conducive to UK cold winter! [/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
[color=rgb(40,40,40)][font='Open Sans'][size=3][center][b]Summary[/b][/center][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
I favour colder than average winter with at least one month to return a notable -AO figure. At present I favour January with a significant stratospheric warming event to occur during late December/early January based on the strats present situation and a gut feeling, but also Cohens work on when warmings are most likely to occur (see strat thread). February may produce the greatest -AO return based on snow cover analysis. December may prove to be mildest month, although with a disrupted PV, colder spells would seem likely, as shown by the reanalysis. Thank-you for reading [font=wingdings]J[/font][/size][/font][/color]

[color=rgb(40,40,40)][font='Open Sans'][size=3][center][b]Further information[/b][/center][/size][/font][/color]
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Some useful papers for further reading. Or try googling, tons will come up![/size][/font][/color]
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An overview of the QBO at Richter et.al., (2011) 'Influence of the quasi-biennial oscillation and ENSO on the frequency of sudden stratospheric warmings' Or see this [url="http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/qbo/"]link[/url][/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
A good paper where the snow cover/AO linkages are first noted. 'Eurasian snow variability and northern hemisphere climate variability' by Judah Cohen and Dan Entekhabi (1999) [/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
The snow cover theory has been developed by Judah Cohen. See - 'Eurasian Snow Cover Variability and Links with Stratosphere-Troposphere Coupling and Their Potential Use in Seasonal to Decadal Climate Predictions' for more information'[/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
See Martius et al., (2009) 'blocking precursors to sudden stratospheric warming events' for an good overview on the strat and conditions that can cause warming events [/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
See Jaiser et al. (2011) for sea ice feedbacks with the stratosphere. ‘Stratospheric response to Arctic sea ice retreat and associated planetary wave propagation changes’ [/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
See Liu et.al., 2012 for a good overview of arctic sea ice and the influence on blocking patterns/winter snow fall. 'Impact of declining Arctic Sea ice on winter snowfall'[/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
See Francis and Varvus (2012) for an overview of sea ice and its influence on seasonal atmosphere circulation. 'Evidence linking Arctic Amplification to extreme weather in the mid-latitudes'[/size][/font][/color][color=rgb(40,40,40)][font='Open Sans'][size=3]
See Baek-Min et.al., (2014) for a recent study on regional ice loss and the impact on the AO 'weakening of the stratospheric polar vortex by Arctic sea-ice loss'[/size][/font][/color]


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