UItleg over AAM is te vinden in publikaties over de General Circulation of the Earth van Starr, Oort,Lorenz e.a.
Deze Wiki is een aardig begin:http://en.wikipedia.org/wiki/Fluctuations_in_the_length_of_day
Stratosfeer en de invloed op ons weer
Re: Stratosfeer en de invloed op ons weer
Karel schreef:UItleg over AAM is te vinden in publikaties over de General Circulation of the Earth van Starr, Oort,Lorenz e.a.
Deze Wiki is een aardig begin:http://en.wikipedia.org/wiki/Fluctuations_in_the_length_of_day
Dank je, Karel.
Re: Stratosfeer en de invloed op ons weer
AAM staat voor de totale hoeveelheid zonale wind, gewogen voor de dichtheid van de lucht. Het totale impulsmoment (hoeveelheid draaiing) van de aarde+ de lucht er omheen is constant. Als de totale oostwaartse component van wind in de atmosfeer toeneemt, gaat de aarde wat langzamer draaien en omgekeerd. Netto gemiddeld over een langere tijd is de zonale windcomponent over de hele aarde 0, dus er is net zo veel (voor de massa gewogen) oosten- als westenwind.
Omdat de daglengte heel nauwkeurig kan worden gemeten, kan daaruit de AAM worden berekend. Volgens mij heeft AAM geen enkele relatie met het weer bij ons, omdat het de som van alle (dichtheidgewogen) winden in de atmosfeer, dus op alle breedten van -90 tot +90 en alle lengtes van 180 tot +180 graden is.
De lange termijn (orde 10 tallen jaren) fluctuaties hebben niets met variaties in de atmosfeer te maken, maar met overdracht van impulsmoment als gevolg van verschillen in rotatiesnelheid tussen de aardkorst, -mantel en -kern.
Omdat de daglengte heel nauwkeurig kan worden gemeten, kan daaruit de AAM worden berekend. Volgens mij heeft AAM geen enkele relatie met het weer bij ons, omdat het de som van alle (dichtheidgewogen) winden in de atmosfeer, dus op alle breedten van -90 tot +90 en alle lengtes van 180 tot +180 graden is.
De lange termijn (orde 10 tallen jaren) fluctuaties hebben niets met variaties in de atmosfeer te maken, maar met overdracht van impulsmoment als gevolg van verschillen in rotatiesnelheid tussen de aardkorst, -mantel en -kern.
Laatst gewijzigd door Adrie op 07-01-2015 00:29, 1 keer totaal gewijzigd.
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Sebastiaan
- Berichten: 12295
- Lid geworden op: 31-12-1977
Re: Stratosfeer en de invloed op ons weer
Bedankt voor de toelichting Adrie!
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Sebastiaan
- Berichten: 12295
- Lid geworden op: 31-12-1977
Re: Stratosfeer en de invloed op ons weer
Tamara heeft een nieuwe update gegeven, 'we' gaan het volgen.
Some very tentative changes emerging in AAM forecasts which might underpin the hints of a gradual pattern change upstream through the second half of January.
Whilst these forecasts are just GEFS based (and tentative) they do lend some credence in terms of latest METO monthly suggestions based on EPS data
Starting with the here and now first:
GWO has undergone another fast classic -AAM style orbit through phases 1,2,3 and then return back to phases 1,2. Negative frictional torques have led to negative mountain torque, adding yet further easterly momentum in the sub tropics to the atmosphere, compensated by stoking up poleward westerly momentum at mid and higher latitudes.
Net effect? : The fast and furious zonal pattern and invigorated Canadian/Greenland vortex we are witnessing following the brief turn of year vortex split.
As suggested in previous posts, re-initiated Nina imprint to the atmosphere has beefed up sub tropical ridges - and a strong Azores High features in the near and mid term, forcing a dynamic pressure gradient differential between the High pressure to the south and the zonally active jet stream just to the north of Scotland.
This pattern now fully advertised in modelling with the deep lows which threaten Northern areas most especially later this week
Meanwhile, the MJO continues its eastward progress towards the dateline, but convection, as anticipated, still looks set to die before it overwrites the more beneficial downstream phases in the central/eastern Pacific. We should not, imo, therefore expect any significant downstream amplification signal around the mid month period - much as suspected in recent days.
This signal could yet be just delayed rather than cancelled though
Beyond the 10 day time period there are early and uncertain indications that the atmosphere will attempt to scrub westerly momentum from mid and higher latitudes as easterly trades in the tropics show signs of weakening - as negative torque wave lengths become exhausted.
So, although uncertain and FI, these predictions are a logical atmospheric pay-back budget balancing compensation act for sooner or later
.
Resultant rather more positive AAM tendency consequently added to the atmosphere in tandem with a less strong ferrel cell signal, gives fully credible support to FI forecasts of forcing the GWO through phase 4 , and into 5
This Phase progression neutralises Nina tendency in the atmosphere and would take us closer to a more 'Nino friendly' atmospheric signal as we head closer towards the last third of the month and February. Such a signal would better favour ridging of High pressure at better altitude
GWO direction of travel through Phases 4/5 engages positive frictional torque and then subsequent Asian positive mountain torque. Net effect would be to force orbit through to Phases 8/1 and trigger a retrogression of the Pacific pattern and switch from -PNA signal to a more +PNA pattern
With the EPO as a consequence turning more +ve, and pressure falling towards the western US coast, this change of pattern would concur with better downstream amplification feeding eastwards thereafter into the atlantic.
In tandem with pressure rising across the Atlantic as the Azores High is weakened and retrogressed North-Westwards, this gives the support for Greenland/Canadian vortex gravitas to transfer eastwards into Scandinavia.
Such vortex transport would be of even further benefit if longer term stratospheric trends could continue to favour a more favourable split in the Atlantic sector next time around.
Long way off, a lot of uncertainties yet to come, and the atmosphere has to plough quite some furrow yet for a while, but things sure would become much more interesting for the last third of winter.
Such evolution does rather echo a typical weak El Nino winter which is often characteristically 'end-loaded' (final-third) for cold. In that sense, and in the context of the frustrations of the winter so far for snow and cold lovers, this sure would be some compensation.
https://forum.netweather.tv/topic/82208-model-output-discussion-stormy-period-inbound/?p=3107669
http://www.atmos.albany.edu/student/nschiral/research/gwo/gfsgwo_1.png
Some very tentative changes emerging in AAM forecasts which might underpin the hints of a gradual pattern change upstream through the second half of January.
Whilst these forecasts are just GEFS based (and tentative) they do lend some credence in terms of latest METO monthly suggestions based on EPS data
Starting with the here and now first:
GWO has undergone another fast classic -AAM style orbit through phases 1,2,3 and then return back to phases 1,2. Negative frictional torques have led to negative mountain torque, adding yet further easterly momentum in the sub tropics to the atmosphere, compensated by stoking up poleward westerly momentum at mid and higher latitudes.
Net effect? : The fast and furious zonal pattern and invigorated Canadian/Greenland vortex we are witnessing following the brief turn of year vortex split.
As suggested in previous posts, re-initiated Nina imprint to the atmosphere has beefed up sub tropical ridges - and a strong Azores High features in the near and mid term, forcing a dynamic pressure gradient differential between the High pressure to the south and the zonally active jet stream just to the north of Scotland.
This pattern now fully advertised in modelling with the deep lows which threaten Northern areas most especially later this week
Meanwhile, the MJO continues its eastward progress towards the dateline, but convection, as anticipated, still looks set to die before it overwrites the more beneficial downstream phases in the central/eastern Pacific. We should not, imo, therefore expect any significant downstream amplification signal around the mid month period - much as suspected in recent days.
This signal could yet be just delayed rather than cancelled though
Beyond the 10 day time period there are early and uncertain indications that the atmosphere will attempt to scrub westerly momentum from mid and higher latitudes as easterly trades in the tropics show signs of weakening - as negative torque wave lengths become exhausted.
So, although uncertain and FI, these predictions are a logical atmospheric pay-back budget balancing compensation act for sooner or later
.
Resultant rather more positive AAM tendency consequently added to the atmosphere in tandem with a less strong ferrel cell signal, gives fully credible support to FI forecasts of forcing the GWO through phase 4 , and into 5
This Phase progression neutralises Nina tendency in the atmosphere and would take us closer to a more 'Nino friendly' atmospheric signal as we head closer towards the last third of the month and February. Such a signal would better favour ridging of High pressure at better altitude
GWO direction of travel through Phases 4/5 engages positive frictional torque and then subsequent Asian positive mountain torque. Net effect would be to force orbit through to Phases 8/1 and trigger a retrogression of the Pacific pattern and switch from -PNA signal to a more +PNA pattern
With the EPO as a consequence turning more +ve, and pressure falling towards the western US coast, this change of pattern would concur with better downstream amplification feeding eastwards thereafter into the atlantic.
In tandem with pressure rising across the Atlantic as the Azores High is weakened and retrogressed North-Westwards, this gives the support for Greenland/Canadian vortex gravitas to transfer eastwards into Scandinavia.
Such vortex transport would be of even further benefit if longer term stratospheric trends could continue to favour a more favourable split in the Atlantic sector next time around.
Long way off, a lot of uncertainties yet to come, and the atmosphere has to plough quite some furrow yet for a while, but things sure would become much more interesting for the last third of winter.
Such evolution does rather echo a typical weak El Nino winter which is often characteristically 'end-loaded' (final-third) for cold. In that sense, and in the context of the frustrations of the winter so far for snow and cold lovers, this sure would be some compensation.
https://forum.netweather.tv/topic/82208-model-output-discussion-stormy-period-inbound/?p=3107669
http://www.atmos.albany.edu/student/nschiral/research/gwo/gfsgwo_1.png
Laatst gewijzigd door Sebastiaan op 07-01-2015 09:38, 1 keer totaal gewijzigd.
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Sebastiaan
- Berichten: 12295
- Lid geworden op: 31-12-1977
Re: Stratosfeer en de invloed op ons weer
En van zojuist!
Analysis of AAM tendency and GWO pattern for Nov/Dec and Jan (to date), tells us the story of how the winter has been driven so far.
A cyclical winter Nina type atmospheric signal of +NAO courtesy of sub tropical ridging to mid latitudes - and totally inhibitive of amplified MJO cycling beyond the dateline. This, despite a weak El Nino oceanic signal which if in harmony with the atmosphere would teleconnect us to the Siberian SIA feedbacks that were expected to be much more prolific in determining the winter pattern, and would also have given us a much more amplified Atlantic pattern under a winter-time +AAM atmospheric state.
However, much as discussed yesterday evening, this is only the story of the first half of this winter.
Those tentative tell-tale forecasted signs of rising AAM (the green line) , signalling a breakthrough response of the GWO being forced out of negative tendency GWO phases 1,2 and 3 into positive tendency Phase 5 are very important, should they verify, in terms of how a changing atmospheric response to better mirror the background Nino state might impact the NH weather patterns and begin to break us away from the flatter +NAO signal to something colder and more amplified.
Discussion was provided yesterday evening, as to how this might evolve the upstream pattern under such a changing signal.
It might take us to much later in the month and towards February, but it is a start. Anyway, best not get hung up on precise timing - the most important thing right now is that this trend is maintained.
Should this be the case, than we should not worry unduly about the MJO forecasts.
Atmospheric state in better harmony and jive with the oceanic El Nino signal will, in time, do the rest here...
Such as the case was in winter 04/05 under a weak El Nino, when cyclical patterns provided a Christmas toppler and snow to northern and western parts, followed by strong zonality through the first half of January (familiar so far ?) and then better amplification in the second half of January (which gave a NE'rly and snow showers IMBY :wink: )
Ever improving amplification sequences and weakening vorticity over Greenland and Canada thereafter led to the fully blocked pattern during the second half of February and into the first days of March 05.
There is certainly a case for something similar to be possible this season.
Expectations for winter 14/15 have been higher than this obviously - but we have to manage them in terms of the reality of what has happened, and where we are instead
Its still very much a case of the trend needing to be our friend here, before we can buy a new sledge....and then think of waxing it.
One final bit of perspective though - Winter 04/05 did feature an SSW - but it arrived on 16 March.....a week or two after any late season snow had melted....
....Eyes on the stratosphere anyway, to assess the magnitude of Asian MT tropospheric wave break which will occur with any entry of GWO into Phase 5. This would provide a forward extra momentum to the atmospheric forcing of its own to benefit our sector of the NH as we head towards and into February...
.
Analysis of AAM tendency and GWO pattern for Nov/Dec and Jan (to date), tells us the story of how the winter has been driven so far.
A cyclical winter Nina type atmospheric signal of +NAO courtesy of sub tropical ridging to mid latitudes - and totally inhibitive of amplified MJO cycling beyond the dateline. This, despite a weak El Nino oceanic signal which if in harmony with the atmosphere would teleconnect us to the Siberian SIA feedbacks that were expected to be much more prolific in determining the winter pattern, and would also have given us a much more amplified Atlantic pattern under a winter-time +AAM atmospheric state.
However, much as discussed yesterday evening, this is only the story of the first half of this winter.
Those tentative tell-tale forecasted signs of rising AAM (the green line) , signalling a breakthrough response of the GWO being forced out of negative tendency GWO phases 1,2 and 3 into positive tendency Phase 5 are very important, should they verify, in terms of how a changing atmospheric response to better mirror the background Nino state might impact the NH weather patterns and begin to break us away from the flatter +NAO signal to something colder and more amplified.
Discussion was provided yesterday evening, as to how this might evolve the upstream pattern under such a changing signal.
It might take us to much later in the month and towards February, but it is a start. Anyway, best not get hung up on precise timing - the most important thing right now is that this trend is maintained.
Should this be the case, than we should not worry unduly about the MJO forecasts.
Atmospheric state in better harmony and jive with the oceanic El Nino signal will, in time, do the rest here...
Such as the case was in winter 04/05 under a weak El Nino, when cyclical patterns provided a Christmas toppler and snow to northern and western parts, followed by strong zonality through the first half of January (familiar so far ?) and then better amplification in the second half of January (which gave a NE'rly and snow showers IMBY :wink: )
Ever improving amplification sequences and weakening vorticity over Greenland and Canada thereafter led to the fully blocked pattern during the second half of February and into the first days of March 05.
There is certainly a case for something similar to be possible this season.
Expectations for winter 14/15 have been higher than this obviously - but we have to manage them in terms of the reality of what has happened, and where we are instead
Its still very much a case of the trend needing to be our friend here, before we can buy a new sledge....and then think of waxing it.
One final bit of perspective though - Winter 04/05 did feature an SSW - but it arrived on 16 March.....a week or two after any late season snow had melted....
....Eyes on the stratosphere anyway, to assess the magnitude of Asian MT tropospheric wave break which will occur with any entry of GWO into Phase 5. This would provide a forward extra momentum to the atmospheric forcing of its own to benefit our sector of the NH as we head towards and into February...
.
Re: Stratosfeer en de invloed op ons weer
Inderdaad de ogen gericht op de stratosfeer. De temperatuursprong mag er zijn. Ogen ook gericht op de MJO en de eventuele convectie in de Tropical Atlantic de komende 2 weken.
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Sebastiaan
- Berichten: 12295
- Lid geworden op: 31-12-1977
Re: Stratosfeer en de invloed op ons weer
Deze vind ik handig. http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/ALL_emean_phase_full.gif
De amplitude van EC is het minste en bereikt nauwelijks fase 7.
Laatst gewijzigd door Sebastiaan op 08-01-2015 17:43, 1 keer totaal gewijzigd.
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Sebastiaan
- Berichten: 12295
- Lid geworden op: 31-12-1977
-
Sebastiaan
- Berichten: 12295
- Lid geworden op: 31-12-1977
Re: Stratosfeer en de invloed op ons weer
CFS blijft er vol voor gaan en dan krijg je dus dit soort settings
