Let's talk ENSO

[weatherwiz]

The purpose of this thread is not directed towards the discussion of current ENSO state or ENSO forecasting as there is a thread for that in the main form, but the purpose of this thread is to elicit discussion about ENSO and how ENSO may influence, shape, or drive global (or hemispheric) weather patterns. As we know, when it comes to long-range weather forecasting, the state of ENSO is a widely and very popular used index. However, is ENSO all that it is played out to be? It is this question here which drives the creation of this thread.

The most popular metric for measuring ENSO state is the Oceanic-Nino Index (ONI). The CPC defines a La Nina event as 5-consecutive trimonthly periods in which SSTA's within region 3.4 are at least -0.5°C or colder. An EL Nino event is defined as 5-consecutive trimonthly periods in which SSTA's within region 3.4 are at least +0.5C or greater. If neither of these conditions are met, the ENSO state is said to be neutral. While the ONI is the most commonly metric used and perhaps the most universally accepted metric, the ONI is not the only metric available to measure ENSO state. In fact, there are at least 50-different definitions available to define ENSO state. A meteorologist by the name of Eric Webb has done some phenomenal work and research regarding ENSO. His work can be found on the following link 

https://www.webberweather.com/ensemble-oceanic-nino-index.html

Eric Webb has created the Ensemble Oceanic Nino Index. Eric Webb's Ensemble ONI dates back to 1950 (compared to the ONI which dates back to 1950). Eric Webb defines an ENSO event of at least 50% of ENSO definitions met surrounding a particular month, irrespective of the events duration and/or potential discontinuities with adjacent months. (For more on ENSO definitions he explains in detail on his page linked above). 

In order to get started with my contribution to this thread and discussion I have done some work just focusing on La Nina Winters. My hope is to continue such work for EL Nino events as well and even focus outside the winter months. Given I have a love and fascination with long-range weather forecasting, my personal goal is to just develop and enhance those skills, or at the very least, just understand what influences global weather patterns and how those patterns correlate to local weather even better. This initial post is set to look for similarities in ENSO events with a correlation on winter (DJF) temperature anomalies across the northern hemisphere. 

In addition to just classifying an ENSO event, the strength of that particular event is very important as the strength can have a significant impact on the large-scale global pattern (especially in stronger events). The following guidelines (which are the most widely accepted for strength breakdown) were used:

Weak Event: SSTAs +/- 0.5°C to +/- 0.9°C

Moderate Event: SSTAs +/- 1.0°C to +/- 1.4°C

Strong Event: SSTAs >/< +/- 1.5°C

Super-strong: </> +/- 2.0°C

As we all know, every ENSO event is shaped differently (each event has its own "flavor". While the state of ENSO alone is an important consideration the structure if just as, if not, perhaps more important then ENSO state alone. By structure of the ENSO event we're referring to where the core of highest anomalies are present. This can help identify whether a particular event is a west-based event, east-based event, central-based event, or basin-wide. This was something I had always seemingly struggle to do and that's how to classify this breakdown. Upon reading Ray's winter outlook last season, I was heavily influenced by what he had done. I was trying to make such a classification much harder than need be. From Ray's influence this was used as a metric to distinguish between the different structures:

 

Before getting a bit more in-depth into some initial work I want to provide some definitions to yield some context.

1. An event was classified if ANY winter month within the trimonthly data involved a defined La Nina

2. The strength was based on the peak SSTA during the event 

3. Additional notes were added to highlight borderline events - in terms of the event itself, strength, and structure (but this is not incorporated within anything posted here). 

Below is a list of defined La Nina Winters using Eric Webb's Ensemble ONI and the CPC's ONI along with the strength breakdown

Below is a structure breakdown of La Nina Winters using Eric Webb's Ensemble ONI and the CPCs ONI along with a grouping of ENSO phase/structure/ In parenthesis indicates if it is Ensemble ONI defined, CPC defined, or both:

Temperature Anomalies

The first part of this project was solely focusing on temperature anomalies vs. ENSO state. So this is a breakdown of comparing temperature anomalies for the winter as a whole (DJF) based off of ENSO state (as defined by both Ensemble ONI and CPC ONI), and where core SSTA's were located within the ENSO region. This will be expanded to also analyze outgoing longwave radiation anomalies (to pinpoint where convection/subsidence is present), zonal wind anomalies (focus on trade winds and upper-level jet), sea-level pressure anomalies, and more. When it came to assessing temperature anomalies, I wanted to do something different. Due to the state of a warming climate (whether this be human-induced/influence, cyclical, or a combination of both goes beyond the realm of this scope) I didn't feel like we could compare say weak La Nina winter temperature anomalies from the early 1900's to a climatological period of 1981-2010 or the latest, 1990-2020. Using the following website 

https://psl.noaa.gov/data/atmoswrit/map/index.html

I was able to create different climatological periods and choose which period the temperature anomalies were being compared too. I used 20th Century Reanalysis V3 (For Years 1904 to 1981) and NCEP/NCAR R1 (for years 1982 to Present) as my datasets. While Eric Webb's Ensemble ONI data goes back to 1850, the dataset for the variables (temperature) went back to like the 1880's or something. What I did was used the following climatological periods. In parenthesis would be the years used against that climatological period's mean (Note: I also did this in the construction of SSTAs which I can perhaps post in a subsequent post):

In order to save space I will post a GIF of the following (Note: I will focus on just the Ensemble ONI Index here since it's a larger dataset). For now I will only post the All La Nina Winters (DJF) Temperature Anomalies and then post these additional GIFs over the coming days. I also used a consistent legend (-7°F to +7°F with an interval of 10°F).

1. All La Nina Winters (DJF) Temperature Anomalies 

2. Weak La Nina Winter Temperature Anomalies

3. Moderate La Nina Winter Temperature Anomalies

4. Strong/Super-Strong La Nina Winter Temperature Anomalies

5. West-Based La Nina Winter Temperature Anomalies 

6. East-Based La Nina Winter Temperature Anomalies

7. Basin-Wide La Nina Winter Temperature Anomalies 

8. Weak West-Based La Nina Winter Temperature Anomalies

9. Moderate West-Based La Nina Winter Temperature Anomalies

10. Strong/Super-Strong West-Based La Nina Winter Temperature Anomalies

11. Weak East-Based La Nina Winter Temperature Anomalies

12. Moderate East-Based La Nina Winter Temperature Anomalies

13. Strong/Super-Strong East-Based La Nina Winter Temperature Anomalies

14. Weak Basin-Wide La Nina Winter Temperature Anomalies

18. Moderate Basin-Wide La Nina Winter Temperature Anomalies

19. Strong/Super-Strong Basin-Wide La Nina Winter Temperature Anomalies

I'm going to bold this part here as this is likely well-beyond a TLDR post but the point of this is too illustrate a few things: Outside of perhaps moderate west-based La Nina's, weak central-based La Nina's, and Strong/Super-Strong Central-Based La Nina's there actually doesn't appear to be a very strong signal correlating La Nina episodes to temperature anomalies across the Northern Hemisphere. Another point here is when you get into breaking down into finite details the sample-sizes become way too small. So I guess my point is that I have a hypothesis that ENSO (maybe just La Nina) does not have the weight or merit that we once thought it did. 

All La Nina Winters (DJF) Temperature Anomalies. Through the GIF you can see the variations in temperature anomalies which exist. Over the days I'll post the additional GIFs as well. I am hoping this may elicit some awesome discussion/research. You'll notice within the loop that climatological periods change as well as the dataset of computation:

 

[weatherwiz]

(EDITED 09/14/2022)

Weak La Nina Winter Temperature Anomalies:

Moderate La Nina Winter Temperature Anomalies:

Strong/Super-Strong La Nina Winter Temperature Anomalies:

 

[weatherwiz]

(EDITED 09/14/2022)

West-Based La Nina Winter Temperature Anomalies:

East-Based La Nina Winter Temperature Anomalies:

Basin-Wide La Nina Winter Temperature Anomalies:

 

[weatherwiz]

(EDITED 09/14/2022)

Weak West-Based La Nina Winter Temperature Anomalies (Includes Ensemble ONI and ONI Defined Events):

Moderate West-Based La Nina Winter Temperature Anomalies (Includes Ensemble ONI and ONI Defined Events):

Strong and Super-Strong West-Based La Nina Winter Temperature Anomalies:

 

[weatherwiz]

(EDITED 09/14/2022)

Weak East-Based La Nina Winter Temperature Anomalies (Includes Ensemble ONI and ONI Defined Events):

Moderate East-Based La Nina Winter Temperature Anomalies (Includes Ensemble ONI and ONI Defined Events):

Strong and Super-Strong East-Based La Nina Winter Temperature Anomalies (Includes Ensemble ONI and ONI Defined Events):

 

 

[weatherwiz]

(EDITED 09/14/2022)

Weak Basin Wide La Nina Winter Temperature Anomalies:

 

Moderate Basin-Wide La Nina Winter Temperature Anomalies (Includes Ensemble ONI and ONI Defined Events):

Strong and Super-Strong Basin-Wide La Nina Winter Temperature Anomalies (Includes Ensemble ONI and ONI Defined Events):

 

[40/70 Benchmark]

I'll have to look at this more closely when I have more time,  but just a couple of notes.

1 ENSO is an important piece of the puzzle and a good foundational concept from which to build an outlook, but nothing should be considered as operating within a vacuum....and as far as sample size goes, that is an issue with respect to everything. I think the structure of ENSO is too important to disregard due to inadequate sample size...now, maybe an argument can be made to simple bin them by east and west based, as opposed to central, as well? But what I will say is that I consider central based events as basin wide bc its pretty difficult to have a central based event not be basin wide...and attempting ro distinguish between central based and basin wide definitely harkens back to your point with respect to finite details and sample sizes.

2) I use some discretion as far as strength designation....for instance if two el nino events both have a peak ONI of +1.5, but one has an MEI of 1.2 and the other 2, I am listing the 1.2 MEI as moderate and 2 as strong. The intensity of the ocean-atmosphere coupling is a very relevent and strong proxy for ENSO peak strength designation. 

[40/70 Benchmark]

Man, this is right in my wheelhouse...one last thing I'll add for tonight is that I also feel like binning the respective subgroups la Nina's by intensity is too much finite detail that exacerbates the sample size issue. You can list omit the seasons that are awful intensity marches from your final forecast composite and/or take measures accentuate the better marches, like doubling them up in the final composite, etc. Binning them by intensity and structure singularly is enough...IOW, have weak, mod, strong, modoki, central-basin wide (hybrid) and east based composites...you don't need weak east based, mod east based, etc...you can just factor those details into your final forecast.

The cool thing about seasonal forecasts is that they are an art with an inherent level of subjectivity, which is a real paradox given that weather is a science. The data is the only element of the entire process that is objective because the interpretation, application format and presentation are not. The forecaster is the artist, and his/her brush is a methodology that is unique to him/her. It is a tool that has been honed, refined and individualized over time ro be applied to a hemispheric canvass of sorts. It's the synthesis of a plethora of variables that is applied and then expressed through your very own lens. And it is for that reason that it is the ultimate form of self expression and a real oasis of creativity within a see of science. This is why I have taken to it because I hate science, but I like to express myself through writing and this couples that with my winter obsession. 

[It's Always Sunny]

Great stuff, Paul. I just recently posted a bunch of composites on my website as reference but your post comes at a good time. Sorting through the composites I’ve noticed that it is hard to say with conviction that certain ENSO structures frequently correlate to specific winter outcomes (temp/precip anomalies). To me, I am seeing more of a mixed bag of results and due to the small sample size it is hard to completely determine the cause and effect. Even analyzing 500 mb gph anomalies doesn’t always match up with what you would expect. Obviously there are other external factors involved but I now don’t give ENSO state as much weight as I used to. There are so many different flavors of it and this may be another area of research but I feel like the phase evolution of ENSO also may play a role in things (whether it is in a strengthening or weakening state) which is masked by the static indices. I’ll add more musings later when I have the time but just wanted to share my initial thoughts on this because I feel like we are on the same page.

[weatherwiz]

9 hours ago, 40/70 Benchmark said:

I'll have to look at this more closely when I have more time,  but just a couple of notes.

1 ENSO is an important piece of the puzzle and a good foundational concept from which to build an outlook, but nothing should be considered as operating within a vacuum....and as far as sample size goes, that is an issue with respect to everything. I think the structure of ENSO is too important to disregard due to inadequate sample size...now, maybe an argument can be made to simple bin them by east and west based, as opposed to central, as well? But what I will say is that I consider central based events as basin wide bc its pretty difficult to have a central based event not be basin wide...and attempting ro distinguish between central based and basin wide definitely harkens back to your point with respect to finite details and sample sizes.

2) I use some discretion as far as strength designation....for instance if two el nino events both have a peak ONI of +1.5, but one has an MEI of 1.2 and the other 2, I am listing the 1.2 MEI as moderate and 2 as strong. The intensity of the ocean-atmosphere coupling is a very relevent and strong proxy for ENSO peak strength designation. 

 

9 hours ago, 40/70 Benchmark said:

Man, this is right in my wheelhouse...one last thing I'll add for tonight is that I also feel like binning the respective subgroups la Nina's by intensity is too much finite detail that exacerbates the sample size issue. You can list omit the seasons that are awful intensity marches from your final forecast composite and/or take measures accentuate the better marches, like doubling them up in the final composite, etc. Binning them by intensity and structure singularly is enough...IOW, have weak, mod, strong, modoki, central-basin wide (hybrid) and east based composites...you don't need weak east based, mod east based, etc...you can just factor those details into your final forecast.

The cool thing about seasonal forecasts is that they are an art with an inherent level of subjectivity, which is a real paradox given that weather is a science. The data is the only element of the entire process that is objective because the interpretation, application format and presentation are not. The forecaster is the artist, and his/her brush is a methodology that is unique to him/her. It is a tool that has been honed, refined and individualized over time ro be applied to a hemispheric canvass of sorts. It's the synthesis of a plethora of variables that is applied and then expressed through your very own lens. And it is for that reason that it is the ultimate form of self expression and a real oasis of creativity within a see of science. This is why I have taken to it because I hate science, but I like to express myself through writing and this couples that with my winter obsession. 

I figured this would be right up your ally and I am looking forward to some great back-and-forth discussion from you and anyone else. To your first post, I am thrilled you made such a post. I don't want to come across and I don't want to make it seem like I am de-valuing ENSO at all. As you stated, ENSO is an extremely important piece of the puzzle. But you make a great point regarding the sample-sizes...perhaps it would be best to combine central-based and basin-wide. You're totally right, it is extremely difficult to sometimes decipher between the two. Per my breakdown I differentiated central-based from basin-wide from whether the core anomalies where between 120-170 or whether the core anomalies extended into 120-170...ultimately, those fringe ENSO regions are relatively small in comparison. This is a great idea!

I'm also glad you brought up the MEI as the MEI and SOI are also important to take into account when assessing ENSO. Of course there is also the TNI (trans-nino index). I've read papers on the TNI but I am still not sure how to grasp, use, and interpret this index. 

Really great opening posts here! As this is a subject I am trying to do much more studying and analysis on this will be an ever expanding work. This will be expanded to look at teleconnection patterns, stratosphere, etc. 

I am so glad I was provided with that second link I provided where you can create anomalies based on a climo period of your choosing. I think this can yield more accurate results. IMO, comparing temperature anomalies from 1908-1909 to a climo period of 1991-2020 I think will slightly skew the integrity of the 1908-1909. Now I'm sure the differences are not that much. 

[weatherwiz]

2 hours ago, It&#x27;s Always Sunny said:

Great stuff, Paul. I just recently posted a bunch of composites on my website as reference but your post comes at a good time. Sorting through the composites I’ve noticed that it is hard to say with conviction that certain ENSO structures frequently correlate to specific winter outcomes (temp/precip anomalies). To me, I am seeing more of a mixed bag of results and due to the small sample size it is hard to completely determine the cause and effect. Even analyzing 500 mb gph anomalies doesn’t always match up with what you would expect. Obviously there are other external factors involved but I now don’t give ENSO state as much weight as I used to. There are so many different flavors of it and this may be another area of research but I feel like the phase evolution of ENSO also may play a role in things (whether it is in a strengthening or weakening state) which is masked by the static indices. I’ll add more musings later when I have the time but just wanted to share my initial thoughts on this because I feel like we are on the same page.

Thank you! This is why I am really trying to evolve this to incorporate so much more. As Ray stated, ENSO is a critical piece of the puzzle, but it alone is not the overall or biggest driver. There are many other factors which need to be taken into account and consideration and perhaps the greatest challenge of all is gauging and figuring out what is driving the pattern...and more times than not it's not just one "piece" it's a combination of "pieces" and figuring out how all those pieces or interacting and driving is the greatest challenge of all. 

[40/70 Benchmark]

3 hours ago, It&#x27;s Always Sunny said:

Great stuff, Paul. I just recently posted a bunch of composites on my website as reference but your post comes at a good time. Sorting through the composites I’ve noticed that it is hard to say with conviction that certain ENSO structures frequently correlate to specific winter outcomes (temp/precip anomalies). To me, I am seeing more of a mixed bag of results and due to the small sample size it is hard to completely determine the cause and effect. Even analyzing 500 mb gph anomalies doesn’t always match up with what you would expect. Obviously there are other external factors involved but I now don’t give ENSO state as much weight as I used to. There are so many different flavors of it and this may be another area of research but I feel like the phase evolution of ENSO also may play a role in things (whether it is in a strengthening or weakening state) which is masked by the static indices. I’ll add more musings later when I have the time but just wanted to share my initial thoughts on this because I feel like we are on the same page.

Go look at the composite from my outlook last season. There were certainly discernible differences by structure and intensity of ENSO....temp, precip, vertical velocity (forcing) and H5.

[It's Always Sunny]

14 minutes ago, 40/70 Benchmark said:

Go look at the composite from my outlook last season. There were certainly discernible differences by structure and intensity of ENSO....temp, precip, vertical velocity (forcing) and H5.

I'll go back and check it out. For the composites I put together, some have a "general" pattern/look for certain ENSO setups but there are also instances where I saw a mix of different outcomes which I'll follow up with later.

[40/70 Benchmark]

5 minutes ago, It's Always Sunny said:

I'll go back and check it out. For the composites I put together, some have a "general" pattern/look for certain ENSO setups but there are also instances where I saw a mix of different outcomes which I'll follow up with later.

Yea, it's not absolute, but for the most part the mean composite of each season was what one would expect....especially with respect to the more poleward Aleutian ridge for east-based data set. Last season was a prime example....well behaved. 

[40/70 Benchmark]

I feel like using ENSO as a general framework to begin with gives you just about as good a shot of any other arbitrary plethora of indicators. 

[It's Always Sunny]

Going through my ENSO composites and comparing them to Paul's I found that a lot of what I called CP La Nina, Paul calls Basin Wide. I also have no bucket for WP La Nina, where for me those are CP. I don't think this makes a huge difference but I also have my composites running between Nov-Mar to parallel how NOAA PSL does it. In addition, my contour intervals are fixed which allows for specific anomalies to pop out more than the Reanalysis page which could water things down a bit. I don't think either of us or right or wrong but just shows how much subjectivity is out there which could lead to different results. After looking through everything I do think I should sift through my composites again and make sure I have everything in the correct category per the definitions that I think we all three agree on.

[40/70 Benchmark]

17 minutes ago, It&#x27;s Always Sunny said:

Going through my ENSO composites and comparing them to Paul's I found that a lot of what I called CP La Nina, Paul calls Basin Wide. I also have no bucket for WP La Nina, where for me those are CP. I don't think this makes a huge difference but I also have my composites running between Nov-Mar to parallel how NOAA PSL does it. In addition, my contour intervals are fixed which allows for specific anomalies to pop out more than the Reanalysis page which could water things down a bit. I don't think either of us or right or wrong but just shows how much subjectivity is out there which could lead to different results. After looking through everything I do think I should sift through my composites again and make sure I have everything in the correct category per the definitions that I think we all three agree on.

Yea, this is why I suggest grouping basin wide and central together, which is how I do it.

[40/70 Benchmark]

I defined the ones with very little cold east of about 150W as being west based. I link my groupings later. There is subjectivity, which is what I was mentioning last night in my initial ramblings...the data is objective, but the interpretation, synthesis and application is all at least somewhat subjective.

[weatherwiz]

1 hour ago, It&#x27;s Always Sunny said:

Going through my ENSO composites and comparing them to Paul's I found that a lot of what I called CP La Nina, Paul calls Basin Wide. I also have no bucket for WP La Nina, where for me those are CP. I don't think this makes a huge difference but I also have my composites running between Nov-Mar to parallel how NOAA PSL does it. In addition, my contour intervals are fixed which allows for specific anomalies to pop out more than the Reanalysis page which could water things down a bit. I don't think either of us or right or wrong but just shows how much subjectivity is out there which could lead to different results. After looking through everything I do think I should sift through my composites again and make sure I have everything in the correct category per the definitions that I think we all three agree on.

Agreed...there is definitely alot of subjectivity involved because there are really so many different ways you can go about things. I actually thought about doing composites from November-March as well (and that is what I had done in the past) but I wanted to focus more on the primary season and for the reason of November and March there can be a lot of transitioning going on. 

But I'm going to be making these same composites looking at 500 pattern, jet stream, and OLR. I have a feeling and well Ray pretty much indicated as such, you're see much stronger connections here. 

[It's Always Sunny]

I reevaluated my composites and after some thought decided to create a La Niña basinwide section. Most of it matches Paul’s. Didn’t create a WP section since everything I have on my end didn’t fully seem to fit that criteria. I may add some more years to my website however haven’t gotten to evaluating them yet.

[40/70 Benchmark]

47 minutes ago, It&#x27;s Always Sunny said:

I reevaluated my composites and after some thought decided to create a La Niña basinwide section. Most of it matches Paul’s. Didn’t create a WP section since everything I have on my end didn’t fully seem to fit that criteria. I may add some more years to my website however haven’t gotten to evaluating them yet.

I'll show you the years I had for modoki tomorrow.

[40/70 Benchmark]

Here is intensity, save for last season, which I have designated as moderate due to the MEI.

There are definitely differences apparent:

Cool Neutral:

 

 

Weak La Nina: 

 

Moderate La Nina: 

Strong La Nina: 

 

 

[40/70 Benchmark]

Here is some relevant material with respect to the three structural designations from my work last fall, not including last year, which was east based and well behaved with poleward Aleutian ridge that drove the severe mid winter stretch centered on the blizzard....again, clear differences: 

East Pacific (EP) La Ninas

East Pacific events are "characterized by the cooling SST anomaly center confined to the EP

 east of 150°W and relatively weak SST anomaly observed over the CP". They decay

 more quickly overall. These canonical la nina events are theorized to be relegated

 largely to the eastern Pacific due to the fact that they are a byproduct of the

 thermocline dynamics present in the Walker Cycle", which is explained  in the

 ENSO & Tropical Background addendum.

 

Here is a composite of cool ENSO events meeting this criteria:

 

 

 

 

 

Note that the warmer anomalies near the dateline ensure that forcing remains over the central and western Pacific,

 similar to the weaker la nina composite. Sinking air that discourages convective forcing is focused well east of the dateline. Also evident is that the Aleutian ridge focuses more to the northwest relative to the modoki, cp event, which will be illustrated when that particular composite is reviewed. 

This often entails a protrusion of said ridge into the polar region at times, which likely contributes to the lower heights

 over the mid latitudes:

 

 

 

Note again the similarities to the weak la nina H5 composite that was comprised in the intensity segment of the discussion. 

Obviously that is because all of these events were weak, however, there are some stronger basin wide events that were still decidedly biased east. Two such events there were referenced earlier are the strong la nina events of 1955-1956 and 2010-2011, which were both fairly cold across the eastern US and featured a great deal of blocking. Both of these have been designated as mixed-type "hybrid" events.

 

Mixed Type La Nina Explains Why Some Stronger La Nina Events Behave Differently

When the large cooling anomaly occupies both the eastern Pacific and the central Pacific during the mature

 phase of development, we have what is referred to as a mixed type of la nina. These events usually mature on

 average a bit later in January, as opposed to December for EP and CP events, which coincides with the forecast NDJ tri monthly peak of this event. During the maturing stage, the cooling anomaly shifts rapidly from the east

 pacific to the central Pacific. This is precisely how this current event had been evolving throughout the month of September, when region 1.2 dramatically warmed and region 4 cooled. However, this trend has since ceased and even reversed, ensuring that it will remain of the mixed variety and not transition into a modoki.

 

Zhang cites 3 events as meeting this criteria, which are the la ninas of 1970-71, 2007-2008 and 1999-2000. 

However, Eastern Mass Weather has modified this composite to also include other events deemed to be of the basin wide, "mixed type" variety, which includes the strong 1955-1956 and 2010-2011 events.

 

 

Note that the location of the composite maximum anomaly at roughly 130-180* longitude is slightly west of the current placement, between about 120 and 140* longitude, which is consistent with some of the more eastward leaning basin-wide events, such as 1955-1956 and especially 2010-2011.

 

 

 

Here is the 2010-2011 season, which is perhaps the best fit to the current season structurally speaking, though it was significantly stronger.:

 

 

 

The 1955-1956 strong la nina event had the area of maximum anomalies biased even slightly more to the east end of the mixed composite spectrum.

 

Where as a basin wide season such as 2007-2008 had the max anomalies more evenly distributed east and west of 150 degrees longitude, and if anything biased slightly to the west.

 

This season had a notable absence of high latitude blocking and a rather flat Aleutian ridge more redolent of the modoki and strong la nina composite:

 

 

Since the majority of the hybrid seasons in this grouping are more like 2007-2008 and not as biased to the east as 2010-2011 and 1955-1956 respectively, the resultant forcing of the mixed-basin wide composite is fairly dissimilar to the EP composite, which makes sense since the western ENSO flank does have significant negative anomalies.

 

 

 

Here is here is the resultant H5 composite for the mixed la nina data set:

 

There is notably less high latitude ridging and a flatter Aleutian high than noted in the eastern pacific counterpart. 

Let see how this compares to the modoki composite.

 

Central Pacific (CP) La Nina (Modoki)

"The SST anomaly center associated with the CP La Niña is shifted westward into the CP west of 150°W and small cooling SST anomaly is found over the EP".  In contrast to the canonical EP event, which advances somewhat westward to as much as 150* longitude and decays faster, the CP event decays more slowly and remains in place, while propagating only a small amount in either direction". These differences in zonal location of SST anomaly and their evolutions suggest the possibility of different underlying dynamics, which is indeed the case. Modoki la nina are largely the product of a local air-sea interaction that develops and decays in place over the central Pacific. The reduced cooling over the east may also be further attenuated by a modified Walker cycle, according to Zhang, which features a displacement to the west of the easterly trades responsible for upwelling. In the modoki la nina, the EP trades are replaced with an anticyclone, as a direct result of the cool SST anomalies being shifted west to the CP.

As was the case with respect to the first two composites, Eastern Mass Weather has added some seasons to the Zhang et al CP composite. Most notably, the 2011-2012 la nina, which is a prime example of how modoki characteristics can cause a moderate la nina composite to be more reminiscent of a stronger event.

 

If anything, the very mild 2011-2012 (-1.1 peak ONI) season is biased even further west than the above modoki composite, which partially explains why it was even milder than many strong la nina seasons across the eastern US.

 

 

 

Note that the sinking air over the center of the negative SST anomaly in the CP is inimical to forcing in this area when considering the modoki composite.

 

 

 

The EP and WP forcing associated with the "modoki" la nina generally features an inverse pattern from that of a modoki el nino across North America. This resultant N. American pattern is more akin to an east-based, canonical el nino. however, we obviously have the prominent Aleutian high as opposed to the Aleutian low during el nino due to opposite anomalies over the tropical Pacific. The Aleutian high in this composite is appreciably flatter and displaced to the southeast in relation to its canonical counterpart, as alluded to.
 

Note that this composite is completely void of the trace of high latitude blocking evident in the basin wide composite.

 

It should be clear that the primary distinction between the different structural ENSO types is how they interact with and modulate the polar domain, which obviously has a profound impact on the resultant N. American weather pattern during boreal winter. However, before more closely considering the differences with respect to the polar domain, it is important to review the structural differences with respect to ENSO in order to ensure an adequate foundational understanding.

 

Summary of ENSO Types

 

-The simplest way to conceptualize ENSO and its impact over North America is that canonical el nino and la nina events are east-based and a product of the thermocline dynamics associated with the Walker circulation cycle.

- Canonical la nina events are inverse to canonical el nino events, which are usually stronger and favor higher heights over the eastern US during boreal winter. Canonical, east-based la nina events are usually more moderate in intensity due to a faster rate of decay and favor lower heights over the eastern US during winter.

-Modoki are different, as the Japanese term suggests, in that these ENSO events are born of local in-situ thermocline dynamics. Modoki El ninos are usually more moderate in intensity and favor lower heights over the eastern US during boreal winter. This is in contrast to modoki CP la nina, which are usually stronger events due to a slower rate of decay and favor higher winter heights across the eastern US.

-Its also important to remember that there are exceptions within each distinction. 

-There are weak modoki seasons such as 2000-2001 and 2008-2009, the latter of which was a second year la nina, that were cold in the eastern US and featured blocking. 

-There was weak EP seasons such as 2005-2006 that were still mild. 

-There were strong events such as 2010-2011 and 1955-1956 that were cold because they were biased slightly east, while 2011-2012 was exceptionally mild due to its modoki nature, despite being of modest intensity. 

CP Modoki:

In the above Modoki composite, vertical motion is weak over the W Pac and more pronounced over the

E PAC. Descent is very evident over dateline, which discourages convective forcing.

Hybrid:

While descent is still present over the dateline in our hybrid composite, it is MUCH weaker and vertical motion is more focused west.

This is the favored regime this season, with milder intrusions more frequent south of roughly I-80.

Canonical: East Pacific Based:

Descent is displaced east of dateline in the EP composite, which focuses more convection and vertical

 ascent there.

The placement of this vertical ascent favors convective forcing in MJO phases 5-8 more often than

not, which teleconnects to colder weather in the east.

 

Finally, since the significant cool anomalies of the mixed type la nina encompass both the EP and CP, Zhang postulates that the resultant pattern across North America may mix signals of the EP an CP la Nina in terms of the extratropical atmospheric response. This can be inferred from above referenced basin-wide composite given the relatively unremarkable upper air features, which include a modified se ridge and a neutral to subtle negative NAO signature that is presumably the result of muted CP and EP forcing. This can make correctly diagnosing the crucial polar fields, which Zhang identifies as the "dominant climate variability mode", over North America in a season such as this one most challenging.  

 

[CoastalWx]

I know it's not apples to apples...but I find it strange the height anomalies at 500mb are rather tepid on the east coast, compared to the surface temps anomalies. Maybe because the earlier years skewed it a bit when looking at the 81-10 temp baseline? 

[CoastalWx]

This was in reference to Ray's post like 15 min ago. 

[40/70 Benchmark]

8 minutes ago, CoastalWx said:

I know it's not apples to apples...but I find it strange the height anomalies at 500mb are rather tepid on the east coast, compared to the surface temps anomalies. Maybe because the earlier years skewed it a bit when looking at the 81-10 temp baseline? 

 

7 minutes ago, CoastalWx said:

This was in reference to Ray's post like 15 min ago. 

You are referring to the intensity composites....yea, its because of the climo period. I used 1951-2010 for the temps, which will accentuate the positive anomalies due to the more expansive climo period encompassing a cooler overall global canvass several decades ago. However, the H5 composite would only allow me to utilize the 1981-2010 period, which attenuates the positive height anomalies because it excludes that same coolest stretch from several decades ago.

I really wish the H5 composite would allow me to use 1951-2010...I said this to Will the other day.

[40/70 Benchmark]

8 hours ago, It's Always Sunny said:

I reevaluated my composites and after some thought decided to create a La Niña basinwide section. Most of it matches Paul’s. Didn’t create a WP section since everything I have on my end didn’t fully seem to fit that criteria. I may add some more years to my website however haven’t gotten to evaluating them yet.

I feel like you may not be coming up with a modoki composite because your criteria is too stringent and exclusive....ie, are you looking for seasons that did not have any la nina strength (-0.5C or cooler) at all over the central and east Pacific? If you look at the verbiage in my composites, that is a reflection of the criterion that peer reviewed, academic pieces use...like "small cooling" and "weak anomalies" over other sections. IOW, a west based event need not be entirely void of la nina caliber anomalies in regions further east, they just need to be very weak from around 150W points eastward, with the strong emphasis west of 150. It may help to look at the visual SST composites of my three groups for a more vidual representation.

[CoastalWx]

7 minutes ago, 40/70 Benchmark said:

 

You are referring to the intensity composites....yea, its because of the climo period. I used 1951-2010 for the temps, which will accentuate the positive anomalies due to the more expansive climo period encompassing a cooler overall global canvass several decades ago. However, the H5 composite would only allow me to utilize the 1981-2010 period, which attenuates the positive height anomalies because it excludes that same coolest stretch from several decades ago.

I really wish the H5 composite would allow me to use 1951-2010...I said this to Will the other day.

Oh I see..that explains it. It still gives you the idea though. 

[It's Always Sunny]

10 minutes ago, 40/70 Benchmark said:

I feel like you may not be coming up with a modoki composite because your criteria is too stringent and exclusive....ie, are you looking for seasons that did not have any la nina strength (-0.5C or cooler) at all over the central and east Pacific? If you look at the verbiage in my composites, that is a reflection of the criterion that peer reviewed, academic pieces use...like "small cooling" and "weak anomalies" over other sections. IOW, a west based event need not be entirely void of la nina caliber anomalies in regions further east, they just need to be very weak from around 150W points eastward, with the strong emphasis west of 150. It may help to look at the visual SST composites of my three groups for a more vidual representation.

I have several instances where there is a strong emphasis west of 150 but what Paul has in his is west of 170 which I had one borderline instance but nothing else. West of 150 with not much more west of 170W is still a CP La Niña to me.

[40/70 Benchmark]

16 minutes ago, It's Always Sunny said:

I have several instances where there is a strong emphasis west of 150 but what Paul has in his is west of 170 which I had one borderline instance but nothing else. West of 150 with not much more west of 170W is still a CP La Niña to me.

I guess we are just going to have to agree to disagree on this. The anomaly in this composite is centered at like 165-170W, which is pretty far to the west, and that is reflected in the resultant H5 and VP (forcing) composites.