Weak ENSO

[Alpha5]

Looking at some composites, its clear that a weak ENSO state is much more favorable for cold across the central and east us when compared to a stronger enso.

What does a weaker ENSO do to the long-wave pattern (if anything) that causes this? Does a weaker enso correlate to a -AO/NAO?

Thanks in advance

Weak Nino years Weak Nina years

[Alpha5]

el bumpo.

6/7 weak nino years had a -NAO, any thoughts on this would be welcome.

[GaWx]

el bumpo.

6/7 weak nino years had a -NAO, any thoughts on this would be welcome.

I have 6 of the 7 coldest weak Nino's based on Atlanta DJF's with a -NAO. However, I have only 10 of 16 total weak Nino's with a -NAO. So, a -NAO may not be quite as dominant during ALL weak Nino's as you may be thinking. Regardless, the -NAO is, indeed, an important cooling factor during weak Nino's that have it. The same is the case with the -AO. The +PDO also correlates quite well with cold (although there's a bit of a chicken-egg debate about that index). However, weak Nino's with -NAO's, -AO's, and +PDO's have been quite a bit colder as a whole (at least at Atlanta) than all other ENSO phases with the same -NAO, -AO, and +PDO combo including moderate to strong Nino's as well as weak Nina's. So, I vote for tropical forcing from a weak Nino, itself, to be a very important factor which tends to cause a piling on of extra cold when there is a -NAO/-AO/+PDO. You sort of get more "mileage" so to speak from a -NAO/-AO/+PDO combo coldwise when the ENSO is a weak Nino. Go here for more details backing up this idea, if interested:

http://www.americanw...71#entry1403771

[physicsguy21]

Hi all, I'm the new guy I at least think that stronger ENSO periods feature more distinct, or 'amplified' Atmospheric Angular Momentum states (+ or -). I'm not sure how that may tie into the Arctic Oscillation, but perhaps it has to do with the loosy goosy nature of the MJO/MMW activity in weaker ENSOs?

[usedtobe]

I have 6 of the 7 coldest weak Nino's based on Atlanta DJF's with a -NAO. However, I have only 10 of 16 total weak Nino's with a -NAO. So, a -NAO may not be quite as dominant during ALL weak Nino's as you may be thinking. Regardless, the -NAO is, indeed, an important cooling factor during weak Nino's that have it. The same is the case with the -AO. The +PDO also correlates quite well with cold (although there's a bit of a chicken-egg debate about that index). However, weak Nino's with -NAO's, -AO's, and +PDO's have been quite a bit colder as a whole (at least at Atlanta) than all other ENSO phases with the same -NAO, -AO, and +PDO combo including moderate to strong Nino's as well as weak Nina's. So, I vote for tropical forcing from a weak Nino, itself, to be a very important factor which tends to cause a piling on of extra cold when there is a -NAO/-AO/+PDO. You sort of get more "mileage" so to speak from a -NAO/-AO/+PDO combo coldwise when the ENSO is a weak Nino. Go here for more details backing up this idea, if interested:

http://www.americanw...71#entry1403771

Larry,

Another possibility has to do with ssw events which are more likely during el ninos than la ninas as the tropical forcing strenghtens the brewer dobson circulation. During strong ninos there may be so much convection that the water vapor starts destroying ozone which would then interfere with the warming in the stratosphere more than in a weaker nino. I'm just speculating and don't really know. 2009-2010 was a pretty strong nino with a potent negative ao and NAo so it's probably not that simple. Maybe HM or someone with a better understanding of it might post their thoughts.

[WxMidwest]

There is a niche indicator during El Nino winters and if the NAO will be Negative/Positive, it has worked rather well since 1951, better then ATL tripole, better then ENSO strength comparisons, better then a precursing POL index scheme..

[usedtobe]

There is a niche indicator during El Nino winters and if the NAO will be Negative/Positive, it has worked rather well since 1951, better then ATL tripole, better then ENSO strength comparisons, better then a precursing POL index scheme..

I'm not sure what you mean by niche indicator.

[HM]

Larry,

Another possibility has to do with ssw events which are more likely during el ninos than la ninas as the tropical forcing strenghtens the brewer dobson circulation. During strong ninos there may be so much convection that the water vapor starts destroying ozone which would then interfere with the warming in the stratosphere more than in a weaker nino. I'm just speculating and don't really know. 2009-2010 was a pretty strong nino with a potent negative ao and NAo so it's probably not that simple. Maybe HM or someone with a better understanding of it might post their thoughts.

The strength of El Niño is a factor but not as important as the stratospheric indicators and "base" of the SST anomalies. The stratospheric players are much more pronounced during El Niño than La Niña, mainly for the reasons you've described already. Therefore, the HT relationships and upper level zonal wind anomalies are more effective during this ENSO state. A west-based El Nino will, for the most part, produce a pretty cold picture for the eastern two thirds of America, especially in December and February. Of course, there are exceptions (94-95 is a notable fail).

Usually the west based El Ninos that failed had poor stratospheric conditions, either from a poor HT relationship standpoint or the warm ENSO was long enough to exhaust a lot of the available ozone.

[WxMidwest]

I'm not sure what you mean by niche indicator.

There is another indicator (Wx Variable at some Point/Box Long/Latitude) That has an impressive track record in predicting The NAO for Winter well before Winter Starts, but it only works for El Nino periods...

[HM]

There is another indicator (Wx Variable at some Point/Box Long/Latitude) That has an impressive track record in predicting The NAO for Winter well before Winter Starts, but it only works for El Nino periods...

If you are being purposely vague, I hope I'm not screwing that up for you but I think you are referring to that impressive SLP technique in the Pacific Ocean you developed. That thing kicks major arse if I remember some of the old forecasts correctly.

Looking forward to your work.

[WxMidwest]

HM, this is true, that being said, it seems that existing areas of forcing and precursors for La Nina/Neutral Analogs seem much harder to find because of the very reasons you sited in #8 of this thread. I'm still on and off researching a complete algorithm for the DJF/DJFM NAO. Off subject a little here, did you start a new blog on blogspot?

[usedtobe]

The strength of El Niño is a factor but not as important as the stratospheric indicators and "base" of the SST anomalies. The stratospheric players are much more pronounced during El Niño than La Niña, mainly for the reasons you've described already. Therefore, the HT relationships and upper level zonal wind anomalies are more effective during this ENSO state. A west-based El Nino will, for the most part, produce a pretty cold picture for the eastern two thirds of America, especially in December and February. Of course, there are exceptions (94-95 is a notable fail).

Usually the west based El Ninos that failed had poor stratospheric conditions, either from a poor HT relationship standpoint or the warm ENSO was long enough to exhaust a lot of the available ozone.

Thanks fro chiming in.

[HM]

HM, this is true, that being said, it seems that existing areas of forcing and precursors for La Nina/Neutral Analogs seem much harder to find because of the very reasons you sited in #8 of this thread. I'm still on and off researching a complete algorithm for the DJF/DJFM NAO. Off subject a little here, did you start a new blog on blogspot?

Yes. The address is: ionlyusethegfs.blogspot.com

I will try and update it once a week but I will not always be able to and this may be one of those weeks.

[HM]

Thanks fro chiming in.

No problem.

[GaWx]

The strength of El Niño is a factor but not as important as the stratospheric indicators and "base" of the SST anomalies. The stratospheric players are much more pronounced during El Niño than La Niña, mainly for the reasons you've described already. Therefore, the HT relationships and upper level zonal wind anomalies are more effective during this ENSO state. A west-based El Nino will, for the most part, produce a pretty cold picture for the eastern two thirds of America, especially in December and February. Of course, there are exceptions (94-95 is a notable fail).

Usually the west based El Ninos that failed had poor stratospheric conditions, either from a poor HT relationship standpoint or the warm ENSO was long enough to exhaust a lot of the available ozone.

This brings back memories of some good discussions done in 5/2009. (Aside: the best ENSO discussions seem to occur in May lol). From then, I had compiled this list showing Nino winters 1950-2009 going from coldest to warmest for E half of US:

Yr. Started/East, West, or Neutral Based/Strength

1) 76: E/W

2) 77: W/W

3) 69: E/W

4) 63: N/W

5) 02: W/M

6) 57: N/S

7) 68: W/W

8) 65: E/S

9) 87: W/S

10) 86: N/M

11) 04: W/W

12) 72: E/S

13) 82: E/S

14) 94: W/M

15) 06: N/M

16) 91: E/S

17) 51: E/W

18) 97: E/S

These were my conclusions:

- Four coldest (bolded) are weak and only one (77-78) is west based. Two of three coldest are east based.

- Despite two of three coldest being east based, stats say west as a group colder than east as a group...note three warmest all east based....but stats also say weak as a group colder than west as a group,

So, my point then was that I agreed that west based have been colder than east based Nino's but I also felt that strength of Nino has been MORE, not less, of a determining factor than east vs. west.

Since then we had a strong Nino in 2009-10, which I'm calling slightly west-based. It was actually east based in Dec. but west based in Jan.-Feb. It averages somewhat west based imo. That winter was, indeed, a cold one and close to the coldest strong Nino on record for especially the SE US. So, admittedly, this helps the cause to some extent of those supporting east vs. west based being the strongest factor. However, I believe that 2009-10 would still only be about 5th on the coldest list, thus leaving the four coldest as weak Nino's with two of those being east-based and only one being west-based. So, I still feel that strength has somewhat more influence than east vs. west based on the overall stats.

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I used this ONI chart to determine strength of Nino's:

http://www.cpc.ncep....000_climo.shtml

[H2Otown_WX]

This brings back memories of some good discussions done in 5/2009. (Aside: the best ENSO discussions seem to occur in May lol). From then, I had compiled this list showing Nino winters 1950-2009 going from coldest to warmest for E half of US:

Yr. Started/East, West, or Neutral Based/Strength

1) 76: E/W

2) 77: W/W

3) 69: E/W

4) 63: N/W

5) 02: W/M

6) 57: N/S

7) 68: W/W

8) 65: E/S

9) 87: W/S

10) 86: N/M

11) 04: W/W

12) 72: E/S

13) 82: E/S

14) 94: W/M

15) 06: N/M

16) 91: E/S

17) 51: E/W

18) 97: E/S

These were my conclusions:

- Four coldest (bolded) are weak and only one (77-78) is west based. Two of three coldest are east based.

- Despite two of three coldest being east based, stats say west as a group colder than east as a group...note three warmest all east based....but stats also say weak as a group colder than west as a group,

So, my point then was that I agreed that west based have been colder than east based Nino's but I also felt that strength of Nino has been MORE, not less, of a determining factor than east vs. west.

Since then we had a strong Nino in 2009-10, which I'm calling slightly west-based. It was actually east based in Dec. but west based in Jan.-Feb. It averages somewhat west based imo. That winter was, indeed, a cold one and close to the coldest strong Nino on record for especially the SE US. So, admittedly, this helps the cause to some extent of those supporting east vs. west based being the strongest factor. However, I believe that 2009-10 would still only be about 5th on the coldest list, thus leaving the four coldest as weak Nino's with two of those being east-based and only one being west-based. So, I still feel that strength has somewhat more influence than east vs. west based on the overall stats.

----------------------------------------------------------------------------

I used this ONI chart to determine strength of Nino's:

http://www.cpc.ncep....000_climo.shtml

Don't you think the solar min. probably had a good deal to do with that winter being as cold as it was?

[GaWx]

Don't you think the solar min. probably had a good deal to do with that winter being as cold as it was?

It is an interesting idea, but not something I can answer. We know that the AO was in record negative territory. Could that have had something to do with the sun? Any opinions? Regardless, my understanding about the sun is that the cold supposedly builds up gradually over a number of years around a grand solar min. So, I'll guess that the sun didn't have a huge direct impact but perhaps a small direct and possibly a bigger indirect impact?

[usedtobe]

It is an interesting idea, but not something I can answer. We know that the AO was in record negative territory. Could that have had something to do with the sun? Any opinions? Regardless, my understanding about the sun is that the cold supposedly builds up gradually over a number of years around a grand solar min. So, I'll guess that the sun didn't have a huge direct impact but perhaps a small direct and possibly a bigger indirect impact?

When you look back at a year it's always easy to attribute why it was so anomalous based on preconceived notions that may or may not be right. That said, what went on in the stratosphere as early as November may have preconditioned the atmosphere making it easier to get a strongly negative AO. There was a warming event in November that weakened the polar vortex. Then there was another warming event in January that reinforced the negative AO. Such warming events in Jan are more likely with a easterly QBO with a el nino which presumably deepens the convection. strengthens the brewer dobson circulation to transport Ozone towards the poles. The until the influx of h20 starts destroying the ozone, you get warming over the high latitudes. At least that's a simplistic version of what might have contributed to the negative AO.

Warming events in winter are also more likely during an easterly QBO when the solar flux is low.

Of course, it may have also been serendipity or just dumb luck. That's the tough thing about working with short data sets and trying to glean what may have occurred when the physics still is not really understood that well

[Quixotic1]

So if Smin and Easterly QBO = early SSW while Smax and Westerly QBO = late SSW, what happens when you have an approaching Smax with a - QBO, which seems to be the case for the upcoming winter? Even though we are approaching the Smax for Cycle 24, it is much weaker than previous cycles (similar to Cycle 20). Would this impact it in any way? My questions are based upon all other things being equal.

[usedtobe]

So if Smin and Easterly QBO = early SSW while Smax and Westerly QBO = late SSW, what happens when you have an approaching Smax with a - QBO, which seems to be the case for the upcoming winter? Even though we are approaching the Smax for Cycle 24, it is much weaker than previous cycles (similar to Cycle 20). Would this impact it in any way? My questions are based upon all other things being equal.

That's a good question, one I can't answer and the qbo solar uncertainty is one of the reasons that this winter making a call about blocking and snowfall is a tricky call.

[Quixotic1]

That's a good question, one I can't answer and the qbo solar uncertainty is one of the reasons that this winter making a call about blocking and snowfall is a tricky call.

Thanks for your response. After comparing the last two winters, the qbo and solar aspects are intriguing.