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#1436999 - 13/10/2017 22:44 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: KevD]
Seira Offline
Meteorological Motor Mouth

Registered: 27/08/2003
Posts: 7103
Loc: Adelaide Hills.
Originally Posted By: KevD
Originally Posted By: _Johnno_
What on earth is going on?

2016 SAM goes mostly Positive bar the odd temporary wild swing late Autumn and Winter and early Spring then comes in October and goes negative rest of Spring and through Summer til March before going back to Positive again.

2017 SAM generally positive most of Autumn and Winter bar a one or two weeks where it went negative.. It continued to be positive into September... Then we enter October and this?

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/aao/new.aao_index_ensm.html

Surely not the same pattern as last yr? Can't work out why the SAM stays predominantly positive in the cooler months then negative in the warmer months? Love to know what is going on here.



Does anyone have any thoughts on this? Anyone?? Or we to busy arguing about other stuff to see what other posters post in here?

Ok smile :
The SAM as in the one measured by normalised (averaged) SLP differences between 40 and 65 degrees South of the Equator I think smile would be largely governed by the extent to which tropical plumes [via the 576-thickness contour] impinge on the Sub-Tropical Ridge (STR) (at middle-to-high levels of the troposphere). One may notice on any publicly available model the extent to which the 576-to-540-thickness contour-range follows (waves around on) the isobars of the STR. Generally (as far as I can tell), the further north the SAM SLP differences influence, the less impinging the 576-thickness contour does, and the cooler and shallower the troposphere. As the 576 encroaches more [south], the difference between a deeper (warmer) and shallower (cooler) troposphere increases, and moisture, when it moves, encounters rougher (steeper) temperature and wind gradients, hence more variable MSLP and precipitation smile .

That is how I'm describing what I'm observing. If someone can interpret the above into SAM, ENSO IOD, PDO,... great!


Edited by Seira (13/10/2017 22:46)

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#1437132 - 14/10/2017 19:02 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
Seira Offline
Meteorological Motor Mouth

Registered: 27/08/2003
Posts: 7103
Loc: Adelaide Hills.
It's pretty clear the trough has water in it...but who is willing to drink from it? Sorry, but my impression is some of the dialogue in here doesn't pass the sniff test.


Edited by Seira (14/10/2017 19:06)

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#1437141 - 14/10/2017 19:45 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: Seira]
snowbooby Offline
Weather Freak

Registered: 11/05/2016
Posts: 105
Originally Posted By: Seira
Originally Posted By: KevD
Originally Posted By: _Johnno_
What on earth is going on?

2016 SAM goes mostly Positive bar the odd temporary wild swing late Autumn and Winter and early Spring then comes in October and goes negative rest of Spring and through Summer til March before going back to Positive again.

2017 SAM generally positive most of Autumn and Winter bar a one or two weeks where it went negative.. It continued to be positive into September... Then we enter October and this?

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/aao/new.aao_index_ensm.html

Surely not the same pattern as last yr? Can't work out why the SAM stays predominantly positive in the cooler months then negative in the warmer months? Love to know what is going on here.



Does anyone have any thoughts on this? Anyone?? Or we to busy arguing about other stuff to see what other posters post in here?

Ok smile :
The SAM as in the one measured by normalised (averaged) SLP differences between 40 and 65 degrees South of the Equator I think smile would be largely governed by the extent to which tropical plumes [via the 576-thickness contour] impinge on the Sub-Tropical Ridge (STR) (at middle-to-high levels of the troposphere). One may notice on any publicly available model the extent to which the 576-to-540-thickness contour-range follows (waves around on) the isobars of the STR. Generally (as far as I can tell), the further north the SAM SLP differences influence, the less impinging the 576-thickness contour does, and the cooler and shallower the troposphere. As the 576 encroaches more [south], the difference between a deeper (warmer) and shallower (cooler) troposphere increases, and moisture, when it moves, encounters rougher (steeper) temperature and wind gradients, hence more variable MSLP and precipitation smile .

That is how I'm describing what I'm observing. If someone can interpret the above into SAM, ENSO IOD, PDO,... great!




SAM = P*40S P*65S

Normalised monthly zonal pressure differences.

Does have shortcomings like many of its fellow indices and models.

If the pressure at either latitude alters nonsynchronously with the other the index alters - positive means relatively higher value of P*65South in relation to P*40South and negative vice versa - pardon if this is already known to the reader.

I think the normalised bit in the above, takes out the component of variability due to seasonallity.

The original question-
Can't work out why the SAM stays predominantly positive in the cooler months then negative in the warmer months? may be a bit of a red herring - cooler and/or warmer months where exactly? may be more relevant.


Edited by snowbooby (14/10/2017 19:47)

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#1437254 - 15/10/2017 11:27 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: snowbooby]
snowbooby Offline
Weather Freak

Registered: 11/05/2016
Posts: 105
Originally Posted By: snowbooby


SAM = P*40S P*65S

Normalised monthly zonal pressure differences.

Does have shortcomings like many of its fellow indices and models.

If the pressure at either latitude alters nonsynchronously with the other the index alters - positive means relatively higher value of P*65South in relation to P*40South and negative vice versa - pardon if this is already known to the reader.

I think the normalised bit in the above, takes out the component of variability due to seasonallity.

The original question-
Can't work out why the SAM stays predominantly positive in the cooler months then negative in the warmer months? may be a bit of a red herring - cooler and/or warmer months where exactly? may be more relevant.


The above may be misleading. I've found a couple of sources which appear to be contradictory. Will post once resolved.

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#1437257 - 15/10/2017 11:46 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: Mike Hauber]
S .O. Offline
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Registered: 31/01/2011
Posts: 1530
Loc: Southern Victoria
Mike ,
The NW Pacific is fast approaching or maybe even past its significant influence in the feedbacks on the Atmosphere . So we are going to see the Sth Hem / Western Pacific ( which is more of a reference to Indonesia and Austral waters .

So I cant see that NW region driving too many feedbacks in the coming weeks .

As for the SAM , I believe that the Nodal LWT will be deflected in part by the ENSO setup in Eastern Australlia . The SAM and the frontal progressions will most likely concentrate where the Tropical SSTs are more conclusive to where their will be less longitude life blocking . Atleast in repitiveness . The ACPW should effect this and to some extent it looks okay going forward . The dynamic mixing will make it harder to predict what classical setups may deliver in the way of Frontal progressions , aligned troughs and water vapour infeeds .
As for the Antarctic sea ice hole , if 1974-75 is anything to go by it says that if the whole is water current driven and not some unknown upper atmospheric deficiency . Then we are in for a radical ride .
Lastly the waters Sth of the Equator in the Far East will have fast warming as the now continual pattern of suppressed OLR will result in that warming fast in the coming months . More importantly is the constant conveyor of more sub surface driven gyre and the actual Sth Pacific gyre continually pushing this warming water west .
As for down here , violent transitions between cool , warm , wet and dry should be the order of the day for the next two months . Regardless of ENSOs resultant ( which to me is still clear ) , the summer should be cooler .
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#1437261 - 15/10/2017 12:25 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
Snowy Hibbo Offline
Weather Freak

Registered: 30/12/2016
Posts: 312
Loc: Matlock, Victoria.
I just completed a write up on Climate Drivers. While it is primarily based on the Northern Hemisphere, I did a section on ENSO, that may or may not be of interest here.
https://goo.gl/HFrx8a

And in answer to the SAM questions, I did a write up on that a while ago. It may or may not be of use here.
https://longrangesnowcenter.blogspot.com.au/2017/03/southern-annular-mode.html


Edited by Snowy Hibbo (15/10/2017 12:32)
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#1437263 - 15/10/2017 12:28 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
Snowy Hibbo Offline
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Registered: 30/12/2016
Posts: 312
Loc: Matlock, Victoria.

180hr PV 10HPa Forecast EC.
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#1437264 - 15/10/2017 12:50 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
mammatus meestrus Offline
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Registered: 20/11/2008
Posts: 26
Loc: lennox head
Could you give a brief summary of your understanding of the above please Snowy and how it relates to the current discussion.

Cheers.

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#1437270 - 15/10/2017 13:42 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: mammatus meestrus]
Snowy Hibbo Offline
Weather Freak

Registered: 30/12/2016
Posts: 312
Loc: Matlock, Victoria.
Originally Posted By: mammatus meestrus
Could you give a brief summary of your understanding of the above please Snowy and how it relates to the current discussion.

Cheers.

What do you mean above? My articles, or the PV map, or the other discussion?
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#1437290 - 15/10/2017 15:48 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
Kino Offline
Weatherzone Addict

Registered: 10/08/2017
Posts: 1012
Loc: Wollongong, NSW, Aus
The diagram.

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#1437314 - 15/10/2017 17:22 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: S .O.]
Mike Hauber Offline
Weatherzone Addict

Registered: 13/07/2007
Posts: 2711
Loc: Buderim
Originally Posted By: S .O.
Mike ,
The NW Pacific is fast approaching or maybe even past its significant influence in the feedbacks on the Atmosphere . So we are going to see the Sth Hem / Western Pacific ( which is more of a reference to Indonesia and Austral waters .


Not sure why you think this. We are maybe two months away from SH tropical convection season firing up and taking the focus of tropical convection into the southern hemisphere. If anything we are entering a period where the NW Pacific is more important because tropical convection is more likely to be closer to the equator where it can have a strong influence, and less likely to be far north near Japan having no influence.

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#1437332 - 15/10/2017 18:12 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: Kino]
Snowy Hibbo Offline
Weather Freak

Registered: 30/12/2016
Posts: 312
Loc: Matlock, Victoria.
Originally Posted By: Kino
The diagram.

It shows the weakening of the polar vortex, as normally happens at this time of year.
The chart shows the temperature at the heights of 10hPa.

This JMA dataset shows a 'SSW' over September and the last couple of weeks showing a period of stable temperatures.


Edited by Snowy Hibbo (15/10/2017 18:15)
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#1437348 - 15/10/2017 19:07 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
Seira Offline
Meteorological Motor Mouth

Registered: 27/08/2003
Posts: 7103
Loc: Adelaide Hills.
I think I understand what Snowy Hibbo is presenting; without the 'SSW', the trend would not be back to the faded line.

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#1437353 - 15/10/2017 19:24 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: snowbooby]
snowbooby Offline
Weather Freak

Registered: 11/05/2016
Posts: 105
Originally Posted By: snowbooby
Originally Posted By: snowbooby


SAM = P*40S P*65S

Normalised monthly zonal pressure differences.

Does have shortcomings like many of its fellow indices and models.

If the pressure at either latitude alters nonsynchronously with the other the index alters - positive means relatively higher value of P*65South in relation to P*40South and negative vice versa - pardon if this is already known to the reader.

I think the normalised bit in the above, takes out the component of variability due to seasonallity.

The original question-
Can't work out why the SAM stays predominantly positive in the cooler months then negative in the warmer months? may be a bit of a red herring - cooler and/or warmer months where exactly? may be more relevant.


The above may be misleading. I've found a couple of sources which appear to be contradictory. Will post once resolved.


1.This mode describes low frequency variability of the Southern Hemisphere extratropics. A positive index (lower polar pressure) is associated with weaker, zonal winds in the extratropics. A negative value is associated with stronger zonal winds.

https://www.esrl.noaa.gov/psd/data/20thC_Rean/timeseries/monthly/SAM/


2. The Southern Annular Mode (SAM) is the principal mode of variability in the Southern Hemisphere (SH) extra-tropics, describing ~30% of SH climate variability. Its spatial structure comprises synchronous pressure anomalies of opposite sign in mid and high latitudes: when pressures are anomalously high over Antarctica the SAM is defined as being in its positive phase and vice versa

Marshall, Gareth & National Center for Atmospheric Research Staff (Eds). Last modified 10 Jun 2016. "The Climate Data Guide: Marshall Southern Annular Mode (SAM) Index (Station-based)." Retrieved from https://climatedataguide.ucar.edu/climat...-station-based.


My bolding. Anyone able to clarify?

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#1437394 - 15/10/2017 21:40 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: Seira]
Snowy Hibbo Offline
Weather Freak

Registered: 30/12/2016
Posts: 312
Loc: Matlock, Victoria.
Originally Posted By: Seira
I think I understand what Snowy Hibbo is presenting; without the 'SSW', the trend would not be back to the faded line.

Yes the warming of the Stratosphere was abnormally fast during September. They call this a Sudden Stratospheric Warming or SSW. I am not sure if they call it that for the Southern Hemisphere, as we get it very seldom down here compared to the Northern Hemisphere.
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#1437412 - 15/10/2017 22:30 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: Snowy Hibbo]
Seira Offline
Meteorological Motor Mouth

Registered: 27/08/2003
Posts: 7103
Loc: Adelaide Hills.
Originally Posted By: Snowy Hibbo
Originally Posted By: Seira
I think I understand what Snowy Hibbo is presenting; without the 'SSW', the trend would not be back to the faded line.

Yes the warming of the Stratosphere was abnormally fast during September. They call this a Sudden Stratospheric Warming or SSW. I am not sure if they call it that for the Southern Hemisphere, as we get it very seldom down here compared to the Northern Hemisphere.

Bold - That may have to do with topography, and the difference in land area in the north.

I agree that without the stability of the temperature in the 10-hPa vicinity, things could be very different too.


Edited by Seira (15/10/2017 22:31)

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#1437413 - 15/10/2017 22:32 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: Snowy Hibbo]
snowbooby Offline
Weather Freak

Registered: 11/05/2016
Posts: 105
Originally Posted By: Snowy Hibbo
Originally Posted By: Seira
I think I understand what Snowy Hibbo is presenting; without the 'SSW', the trend would not be back to the faded line.

Yes the warming of the Stratosphere was abnormally fast during September. They call this a Sudden Stratospheric Warming or SSW. I am not sure if they call it that for the Southern Hemisphere, as we get it very seldom down here compared to the Northern Hemisphere.


There's a distinction made between major and minor warmings - we do get the latter though I'm not sure of frequency - has to involve a rise of at least 25c in temp in a week or less(this year would have gotten over that threshold I think?) - doesn't has to involve a reversal of westerlies on the stratospheric southern polar vortex perimeter(which is the case with major warming).

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#1437427 - 16/10/2017 00:07 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: ColdFront]
Mega Offline
Meteorological Motor Mouth

Registered: 03/02/2003
Posts: 6551
Loc: Maryborough, Wide Bay, QLD
GFS Extended has been predicting a fairly large WWB at the end of its run for a few days now. Let's hope it doesn't eventuate.

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#1437457 - 16/10/2017 09:25 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: Seira]
Snowy Hibbo Offline
Weather Freak

Registered: 30/12/2016
Posts: 312
Loc: Matlock, Victoria.
Originally Posted By: Seira
Originally Posted By: Snowy Hibbo
Originally Posted By: Seira
I think I understand what Snowy Hibbo is presenting; without the 'SSW', the trend would not be back to the faded line.

Yes the warming of the Stratosphere was abnormally fast during September. They call this a Sudden Stratospheric Warming or SSW. I am not sure if they call it that for the Southern Hemisphere, as we get it very seldom down here compared to the Northern Hemisphere.

Bold - That may have to do with topography, and the difference in land area in the north.

I agree that without the stability of the temperature in the 10-hPa vicinity, things could be very different too.

Correct. Topography is probably the reason behind Northern Hemisphere SSWs.
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#1437462 - 16/10/2017 10:09 Re: Climate Driver Discussion 2017 (Enso, IOD, PDO ,SAM etc) [Re: snowbooby]
Snowy Hibbo Offline
Weather Freak

Registered: 30/12/2016
Posts: 312
Loc: Matlock, Victoria.
Originally Posted By: snowbooby
Originally Posted By: Snowy Hibbo
Originally Posted By: Seira
I think I understand what Snowy Hibbo is presenting; without the 'SSW', the trend would not be back to the faded line.

Yes the warming of the Stratosphere was abnormally fast during September. They call this a Sudden Stratospheric Warming or SSW. I am not sure if they call it that for the Southern Hemisphere, as we get it very seldom down here compared to the Northern Hemisphere.


There's a distinction made between major and minor warmings - we do get the latter though I'm not sure of frequency - has to involve a rise of at least 25c in temp in a week or less(this year would have gotten over that threshold I think?) - doesn't has to involve a reversal of westerlies on the stratospheric southern polar vortex perimeter(which is the case with major warming).

Correct.
[img]https://lh3.googleusercontent.com/CHLU8W...Izl_Solrzen7rRO[/img]
This is the Southern Hemisphere 10 hPa Temperature over the past two years. You can see a fairly consistent down in autumn and up in spring trend. Compare that with the Northern Hemisphere.....
[img]https://lh3.googleusercontent.com/BgFdiy...E0Vt-vanhn9GdsL[/img]
You can see the down trend in autumn and the winter low, but then you can see the massive peaks, which are SSWs. And then they go back down. In the Southern Hemisphere, we don't really get proper SSWs.


Edited by Snowy Hibbo (16/10/2017 10:10)
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