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uk.sci.weather (UK Weather) (uk.sci.weather) For the discussion of daily weather events, chiefly affecting the UK and adjacent parts of Europe, both past and predicted. The discussion is open to all, but contributions on a practical scientific level are encouraged. |
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#1
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Have a look at
http://www.climate-uk.com/temp.htm There is a marked periodicity in the top (10-day mean) chart, especially in the westerly index. In previous years periodicities have come and gone pretty quickly, and I can't remember seeing one quite as marked as this. It's not a statistical artifact ... it's easy to remember the westerly spells in early Jan, early Feb, mid-Mar, early to mid April, and late May, and also the blocked spells between. Philip Eden |
#2
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"Philip Eden" philipATweatherHYPHENukDOTcom wrote in message
http://www.climate-uk.com/temp.htm There is a marked periodicity in the top (10-day mean) chart, especially in the westerly index. In previous years periodicities have come and gone pretty quickly, and I can't remember seeing one quite as marked as this. It's not a statistical artifact ... it's easy to remember the westerly spells in early Jan, early Feb, mid-Mar, early to mid April and late May, and also the blocked spells between. I'm sure that I would find this interesting if I could only follow it. Where do you get your backgrounds from? -- Posted via Mailgate.ORG Server - http://www.Mailgate.ORG |
#3
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![]() "Philip Eden" philipATweatherHYPHENukDOTcom wrote in message ... Have a look at http://www.climate-uk.com/temp.htm There is a marked periodicity in the top (10-day mean) chart, especially in the westerly index. In previous years periodicities have come and gone pretty quickly, and I can't remember seeing one quite as marked as this. It's not a statistical artifact ... it's easy to remember the westerly spells in early Jan, early Feb, mid-Mar, early to mid April, and late May, and also the blocked spells between. Philip Eden A 30-35 day oscillation has been reported in the literature in association with N Atlantic sector blocking and retrogression of the jet,this may be a harmonic of a 70 day signal. Causes may be an internal oscillation involving barotropic interaction with topography,probably unlikely in the Atlantic,or interaction of synoptic transients with the mean flow.I'll find some references if you're interested, -- regards, David add '17' to Waghorne to reply |
#4
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"Waghorn" wrote in message
A 30-35 day oscillation has been reported in the literature in association with N Atlantic sector blocking and retrogression of the jet,this may be a harmonic of a 70 day signal. There is an history of inexplicable cycles in weatherlore too. It is difficult to relate it to anything as regular as these things though. This sort of thing. Somewhat unscientifically set out, as a mere collection belying a total lack of research: In Janiveer if the sun appear, March and April pay full dear. January warm, the Lord have mercy! [Because a premature growth of vegetation is liable to suffer severe damage from spring frosts -Editor] (I had thought the editor's comments unlikely. I'd thought it more likely to be a reference to the prevalence of T.B. and influenza.) While frost might damage the cross fertilisation process of some fruit trees it isn’t likely to do worse to any vegetation. I remember once a hard frost took all the leaves off the conker trees where I used to live. They soon grew back.) A summerish January; a winterish spring. If January calends be summery gay, it will be wintry weather until the calends of May. (Well that one was true enough.) A January spring is worth nothing –Scotland. A warm January, a cold May. Not really illuminating but totally inexplicable (if true.) -- Posted via Mailgate.ORG Server - http://www.Mailgate.ORG |
#5
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![]() "Waghorn" wrote in message news:d8cv29 A 30-35 day oscillation has been reported in the literature in association with N Atlantic sector blocking and retrogression of the jet,this may be a harmonic of a 70 day signal. Causes may be an internal oscillation involving barotropic interaction with topography,probably unlikely in the Atlantic, .... the short-range (synoptic / day-to-day scale) effect of the Greenland land/ice mass on N. Atlantic disturbances is accepted (i.e. the Kap Farvel / Cape Farewell distortion), and I believe that in recent years, the whole subject of the interaction with the Northern Hemispheric broadscale flow has been investigated and found to be a fertile subject. Your mention of topography had 'little bells' ringing at the back of my mind of a study that was published several years ago that directly linked the presence of Greenland with distortions in the long-wave pattern, but after a search, I can't come up with that particular entry. However, I did come up with :- http://folk.uio.no/jegill/papers/pet...004_tellus.pdf "Numerical simulations of Greenland's impact on the Northern Hemisphere winter circulation" from which the following is extracted (from the Conclusion):- quote The present study shows that Greenland has a significant impact on the general circulation of the Northern Hemispheric extratropics, at both lower and mid-tropospheric levels. Due to the presence of Greenland, the storm tracks are shifted southward over the North Atlantic and thus the mountain contributes to less precipitation at the western coast of Norway and over the North Atlantic. Greenland has a damming effect on the air mass on its west side, which is cooled down by radiative heat loss during the polar winter, leading to less geopotential thickness in the area and thus less 500-hPa geopotential height than in the simulation without Greenland. The cold air also causes increased baroclinicity over North America leading to an increase in cyclone activity. On the east side of Greenland, the mountain causes higher sea level pressure which is associated with increased geopotential height at the 500-hPa level. The study demonstrates that Greenland’s impact on the general circulation is fundamentally different from the impact of the Rocky Mountains and the Tibetan Plateau. Unlike the case of the classic Rossby wave where westerlies impinge on a major mountain range and a trough is created downstream of the mountain, Greenland’s impact seems mainly to be a perturbation of the flow on the upstream side of the mountain generated by damming of cold low-level air masses. /quote If I understand aright, then we are not looking at the classic 'Rossby-wave' type of distortion of the pattern, but an indirect control on same due to changes in the temperature regimes either side of Greenland. Whilst searching, I also came upon a few links relating climatological regime changes over Greenland (from Ice core evidence) and the Asian monsoon - this implies quite complex and fundamental teleconnections north-to-south as well as west-to-east: who'd be a climate scientist! Martin. |
#6
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Most of the weather lore was based around the people at the time liking
things to follow in 'proper' order, hence a warm January was deemed as foreboding and not how 'it should be' and therefore something sinister was at work, which usually meant that a cold spring would follow as a form of recompense for the disorder. This goes against findings by Lamb who found that in around 70% of the instances, a warm winter is followed by a warm spring and so on until the cycle gets 'broken'. ________________________ Nick G Exe Valley, Devon 50 m amsl "Michael Mcneil" wrote in message news:dc545d140c4aaae1feddb6b12a0b994e.45219@mygate .mailgate.org... "Waghorn" wrote in message A 30-35 day oscillation has been reported in the literature in association with N Atlantic sector blocking and retrogression of the jet,this may be a harmonic of a 70 day signal. There is an history of inexplicable cycles in weatherlore too. It is difficult to relate it to anything as regular as these things though. This sort of thing. Somewhat unscientifically set out, as a mere collection belying a total lack of research: In Janiveer if the sun appear, March and April pay full dear. January warm, the Lord have mercy! [Because a premature growth of vegetation is liable to suffer severe damage from spring frosts -Editor] (I had thought the editor's comments unlikely. I'd thought it more likely to be a reference to the prevalence of T.B. and influenza.) While frost might damage the cross fertilisation process of some fruit trees it isn't likely to do worse to any vegetation. I remember once a hard frost took all the leaves off the conker trees where I used to live. They soon grew back.) A summerish January; a winterish spring. If January calends be summery gay, it will be wintry weather until the calends of May. (Well that one was true enough.) A January spring is worth nothing -Scotland. A warm January, a cold May. Not really illuminating but totally inexplicable (if true.) -- Posted via Mailgate.ORG Server - http://www.Mailgate.ORG |
#7
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![]() "Martin Rowley" "Waghorn" A 30-35 day oscillation has been reported in the literature in association with N Atlantic sector blocking and retrogression of the jet,this may be a harmonic of a 70 day signal. Causes may be an internal oscillation involving barotropic interaction with topography,probably unlikely in the Atlantic, ................................. Your mention of topography had 'little bells' ringing at the back of my mind of a study that was published several years ago that directly linked the presence of Greenland with distortions in the long-wave pattern, but after a search, I can't come up with that particular entry. .................................................. ............................................ Whilst searching, I also came upon a few links relating climatological regime changes over Greenland (from Ice core evidence) and the Asian monsoon - this implies quite complex and fundamental teleconnections north-to-south as well as west-to-east: who'd be a climate scientist! Martin. Yes,I was precising old notes,but at the time I thought-'Wot about Greenland?'. I will look up the original reference and post further if it's illuminating. There is a note about a possible relation to the Madden Julien Oscillation as well, -- regards, David add '17' to Waghorne to reply |
#8
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![]() "Waghorn" I will look up the original reference and post further if it's illuminating. There is a note about a possible relation to the Madden Julien Oscillation as well, The reference is- Plaut&Vautard,Spells of Low Frequency Oscillations and Weather Regimes in the Northern Hemisphere,J Atmospheric Sciences,V53,no2,1994,p210- (not available online unless you purchase from the AMS website) They use Singular Spectrum Analysis of 700Hpa GPH fields .Can't comment on the technique ,.but the paper seems well regarded and cited. Apparently interaction with topography may play a role but is not a sufficient explanation,synoptic eddy forcing is the major player.Particular phasing of the 30-35 day oscillation is found to precede major European-Atlantic blocking,as occurs in the striking pattern pointed out by Philip.This has interesting results for predictability of such blocks. Whether extratropical oscillations precede or lag tropical oscillations was questioned in the nineties.I believe the view now is that at least some precede-the mechanism is the movement of PV anomalies with the Rossby waves equatorward triggering tropical convection.There are of course feedbacks,and tropical heating anomalies are known to effect the downstream long wave pattern. Anyway,as you point out ,there are a multitude of weak teleconnection patterns, -- regards, David add '17' to Waghorne to reply |
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