ENSO Discussion

[Guest happ]

Does long term ocean warming have an effect on the frequencies of El Nino conditions?

 

https://twitter.com/borenbears

 

[Phil]

Does long term ocean warming have an effect on the frequencies of El Nino conditions?

 

https://twitter.com/borenbears

Well, SSTAs in general as well as the ENSO system are both reflections of changes in circulation, heat budget structures, and their pseudo-entropic conduits to equilibration.

 

So it’s not that warm SSTs affect ENSO. It’s that SSTAs and ENSO are affected by the aforementioned changes to relevant boundary conditions.

[Webberweather53]

Does long term ocean warming have an effect on the frequencies of El Nino conditions?

 

https://twitter.com/borenbears

 

In a general hand-wavy sense, increasing global temperatures in the late holocene would actually equate to less frequent NINO conditions because as the hadley cells further expand, they become less efficient and more reminiscent of NINA-esque conditions, there's likely also a lot more to it than we've been able to uncover. The ENS ONI and CPC's ONI that only uses ERSSTv5 use 30-year sliding base periods to try and remove the AGW signal in the data and even if the globe wasn't warming, I would still use a sliding base period or something of the like because they also indirectly make the observational background more relevant to each climate period in the process. This can include (but isn't limited to) the spatiotemporal coverage of observations, types of observational platforms, and magnitude and types of adjustments to these observations, etc.

[Phil]

In a general hand-wavy sense, increasing global temperatures in the late holocene would actually equate to less frequent NINO conditions because as the hadley cells further expand, they become less efficient and more reminiscent of NINA-esque conditions, there's likely also a lot more to it than we've been able to uncover. The ENS ONI and CPC's ONI that only uses ERSSTv5 use 30-year sliding base periods to try and remove the AGW signal in the data and even if the globe wasn't warming, I would still use a sliding base period or something of the like because they also indirectly make the observational background more relevant to each climate period in the process. This can include (but isn't limited to) the spatiotemporal coverage of observations, types of observational platforms, and magnitude and types of adjustments to these observations, etc.

Agree here. The Mid-Holocene is a great example of this warm globe ENSO/z-cell configuration. Persistent weak/moderate La Niña/-PDO type pattern shows up in literally all of the proxy interpolations, with a larger and more coherent WPAC warm pool as well.

 

Many papers suggest that multi-year niños are much more infrequent during warm climate periods. Not sure about super niño frequency, though. Maybe you would know more about that?

[Webberweather53]

Agree here. The Mid-Holocene is a great example of this warm globe ENSO/z-cell configuration. Persistent weak/moderate La Niña/-PDO type pattern shows up in literally all of the proxy interpolations, with a larger and more coherent WPAC warm pool as well.

 

Many papers suggest that multi-year niños are much more infrequent during warm climate periods. Not sure about super niño frequency, though. Maybe you would know more about that?

 

While I'm not entirely sure on the frequency of Super NINOs in a warmer climate and it's not easy to distinguish amongst those in the proxy records, the maximum potential intensity of El Ninos would probably increase barring that the globe warms and we continue along the path we're on w/ a steepening of the near-equatorial Pacific zonal SST gradient and a larger expanse of the basin above the general SST threshold to readily generate convection and thus generate true westerly winds that break down the wind-gravity balance (although some argue that this number also changes somewhat in a warmer climate). If an El Nino reminiscent of 1997-98 were able to completely breakdown this zonal SST gradient in a warmer climate where the SST slope is steeper, it would definitely be capable of becoming more intense. The efficiency of the Hadley Cells may make this more difficult to be realized. However, I don't think it's unreasonable to assume we'd have a higher ceiling even if the frequency of those extraordinary events somehow wasn't much different from today.

[weatherfan2012]

Well, SSTAs in general as well as the ENSO system are both reflections of changes in circulation, heat budget structures, and their pseudo-entropic conduits to equilibration.

So it’s not that warm SSTs affect ENSO. It’s that SSTAs and ENSO are affected by the aforementioned changes to relevant boundary conditions.

interisting that ocean warming was brought up as that is something that Robert Filex tends to talk about quite alot in interviews and in his book and on his site.

[Phil]

Interesting to see the global SST anomaly decreasing in tandem with warming ENSO and the Arctic opening up for the summer. Not something you typically see at this time of year. Or at least not since the 80s/early 90s.

 

[Phil]

[weather girl]

For whatever it's worth, probably nothing, I'm beginning to be a true believer of an El Nino later this year.  

 

 

Odd configuration... you can see the weak Nino forming in the ENSO regions but its uniformly warm to the north of the ENSO regions and cold to the south.

 

[Webberweather53]

We're following the weak-moderate satellite era El Ninos to script thus far, a weak-moderate El Nino still seems like a better call than none at all or a head fake based on what I'm seeing. We are about where I thought we would be several months ago and where we need to be at this point in time to see this solution verify. We'll take our foot momentarily off the gas pedal in the first half of July then the hammer is probably going to come down in late in the month and/or into early August as subseasonal forcing realigns w/ a bgd state that's steadily becoming more NINO like. It's also worth mentioning that most weak-moderate El Ninos in the satellite era were dominated by prolonged periods of easterlies near the dateline before the Equinox but that did little if anything to halt their momentum into the boreal winter. As long as we continue to see WWBs w/ every subseasonal forcing shift into the Pacific, even if there are formidable easterlies for prolonged stretches of time in between, we'll continue moving forward. 

[Phil]

Funny, I actually thought we’d be farther along by now, even in my head-fake scenario. I still can’t find a conduit to the dateline WWB action necessary to pull us over the finish line. Or at least not in time to counter EPAC diffraction.

[Webberweather53]

Funny, I actually thought we’d be farther along by now, even in my head-fake scenario. I still can’t find a conduit to the dateline WWB action necessary to pull us over the finish line. Or at least not in time to counter EPAC diffraction.

 

Most of the satellite era weak-moderate events saw limited dateline WWBs until we got into October and the conduit with most of those events rested on the PMM which is still large and positive atm. I don't see the head fake scenario playing out unless the Atlantic warmed up a lot in the next few months. Considering we just set a new record low -AMM last month, I don't think that's going to happen.

 

[Phil]

Interesting. How do the thermocline sloshes in those years compare to this year re: timing and amplitude?

 

My gut instinct is that our pair of OKWs will complete their half-life cycles ~ 3 weeks before the equinox. That feels like unfavorable timing to me without a WWB/warm pool tap before then. But it’s definitely not a confident prediction.

[Webberweather53]

Interesting. How do the thermocline sloshes in those years compare to this year re: timing and amplitude?

 

My gut instinct is that our pair of OKWs will complete their half-life cycles ~ 3 weeks before the equinox. That feels like unfavorable timing to me without a WWB/warm pool tap before then. But it’s definitely not a confident prediction.

 

Another weak downwelling KW is crossing the International Dateline atm in the wake of these other KWs and we appear to be tapping into the warmpool yet again.

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/ocean/anim/wkxzteq_anm.gif

 

 

In terms of warm water volume along/east of the dateline, we're running close to 2009, 2004, & 2002 atm, and behind 1997 & 2015 obviously. The evolution of thermocline suppression, OKW behavior, and Eq trade wind distribution seems to be closely mirroring 2009 although we have an advantage thus far w/ weaker dateline easterlies.

 

 

July 2002 BOM subsurface analysis

 

http://www.bom.gov.au/archive/oceanography/ocean_anals/IDYOC002/IDYOC002.200207.gif

 

2009

http://www.bom.gov.au/archive/oceanography/ocean_anals/IDYOC002/IDYOC002.200907.gif

 

This year

http://www.bom.gov.au/archive/oceanography/ocean_anals/IDYOC002/IDYOC002.201807.gif

[Phil]

You think there’s enough fluid inertia there to delay the backslosh? I guess we’ll see.

[Webberweather53]

You think there’s enough fluid inertia there to delay the backslosh? I guess we’ll see.

 

When a downwelling Kelvin Wave reaches the eastern boundary, it returns as a slower moving, westward propagating off-equatorial Rossby Wave. This means the "black slosh" from a KW is often much slower and arduous than the other way around. Likewise, when upwelling Rossby Waves generated from a westerly wind anomaly in the CP reaches the western boundary, it returns as an upwelling Kelvin Wave and typically terminates an El Nino.

 

I'm under the impression that you were incorrectly assuming that when a Kelvin Wave reaches South America it returns westward as a Kelvin Wave too and propagates at the same speed as it did before hitting South America and this somehow means it's completed its half cycle.

 

This is actually not true at all.

 

In fact, when a downwelling KW reaches the eastern boundary it's only about 1/4th of the way through it's life cycle because the Rossby Wave that's generated from the Kelvin Wave reflection propagates at one third (~1 m/s) of the Kelvin Wave phase speed (~3 m/s). This also means this backslosh you're referring to due to a refracted Kelvin Wave returning as a Rossby Wave is actually 3x slower than the downwelling Kelvin Wave that triggered it, meaning that it would take about 6 months for a RW generated at the western boundary to return and pass the CP (even then the RW is still suppressing the thermocline because the downwelling KW generates a downwelling RW, both of which constructively interfere w/ one another and generate the quasi-stationary and then eventually the slowly westward propagating SST configuration in the Eq Pacific.). Another KW is crossing the dateline now and will likely reach South America sometime near the beginning of September. It will take about another 5-6 months after that KW hits South America for it to pass the dateline again as Rossby Wave, certainly seems like we're doing fine w/ maintaining forcing thru the solstice.

 

Also keep in mind that NINO termination usually occurs as Rossby Waves refract against the western boundary and return as upwelling Kelvin Waves and not by downwelling RWs being generated at the eastern boundary. There's still a lot of downwelling in the WP atm as yet another weak-moderate Kelvin Wave is passing the dateline and the westerly wind anomalies aren't really that strong (as is often true in most weak-moderate El Ninos). All of this evidence along with what I already discussed in my previous comparisons to satellite era El Ninos does suggest that...

a ) We will not see termination of this event any time soon

b ) We're drawing directly from the West Pac Warm pool w/ another downwelling KW in progress

c ) We do in fact have enough WWB forcing to trigger an El Nino (semi-regular modest WWBs w/ each subseasonal forcing pass is sufficient for weak-moderate El Ninos leading into boreal winter)

d ) a conduit (the strong +PMM) to manipulate and maintain the forcing

[Phil]

When a downwelling Kelvin Wave reaches the eastern boundary, it returns as a slower moving, westward propagating off-equatorial Rossby Wave. This means the "black slosh" from a KW is often much slower and arduous than the other way around. Likewise, when upwelling Rossby Waves generated from a westerly wind anomaly in the CP reaches the western boundary, it returns as an upwelling Kelvin Wave and typically terminates an El Nino.

 

I'm under the impression that you were incorrectly assuming that when a Kelvin Wave reaches South America it returns westward as a Kelvin Wave too and propagates at the same speed as it did before hitting South America and this somehow means it's completed its half cycle.

Sorry, I wasn’t trying to suggest the KW itself refracts back westward upon reaching the EPAC. That wouldn’t make physical sense without some kind of barrier to restrict meridional evacuation. So the bathtub analogy is technically incorrect.

 

But when the OKW reaches the EPAC and diffracts into the two off-equator oceanic rossby waves, it aids equatorial upwelling behind the tail as water evacuates poleward, as I’m sure you know.

 

Hence the importance of a healthy follow-up OKW.

[Jesse]

giphy.gif

Does this count as a healthy follow up OKw?

[OKwx2k4]

Does this count as a healthy follow up OKw?

Guess not. Lol. I'll remove it. Sorry about that. It was a good post. Didn't think a "like" covered it so I did that.

[Phil]

Sorry, I wasn’t trying to suggest the KW itself refracts back westward upon reaching the EPAC. That wouldn’t make physical sense without some kind of barrier to restrict meridional evacuation. So the bathtub analogy is technically incorrect.

 

But when the OKW reaches the EPAC and diffracts into the two off-equator oceanic rossby waves, it aids equatorial upwelling behind the tail as water evacuates poleward, as I’m sure you know.

 

Hence the importance of a healthy follow-up OKW.

And does the +PMM actually aid the development of the niño, or is it largely a result of the low frequency state of circulation that favors warm pool discharges?

 

I’m more convinced of the latter. Too much off-equator convection can actually interfere with El Niño development, in the canonical sense. Some of the most prolific +PMMs like 1980 and 2014 were very anemic in the ENSO department.

[Jesse]

Guess not. Lol. I'll remove it. Sorry about that. It was a good post. Didn't think a "like" covered it so I did that.

Just a joke.

[Webberweather53]

Sorry, I wasn’t trying to suggest the KW itself refracts back westward upon reaching the EPAC. That wouldn’t make physical sense without some kind of barrier to restrict meridional evacuation. So the bathtub analogy is technically incorrect.

 

But when the OKW reaches the EPAC and diffracts into the two off-equator oceanic rossby waves, it aids equatorial upwelling behind the tail as water evacuates poleward, as I’m sure you know.

 

Hence the importance of a healthy follow-up OKW.

 

I see where you're coming from but the latter isn't true either. When a Kelvin wave reflects onto a boundary it returns as a rossby wave of the same sign. Meaning that these downwelling Rossby Waves created by reflection of the KW at the eastern boundary also suppress the thermocline. What actually enhances near-equatorial upwelling during El Nino events is the westward flowing surface currents which are in the same sense as earth's rotation generating cyclonic wind stress curl anomalies that augment Sverdrup transport, in effect increasing poleward export of water from the equator. Those westward propagating off-equatorial Rossby Waves actually do contribute to some extent to retaining heat in the Eq Pacific because their westward propagation contributes to anticyclonic wind stress curl that offsets the Equatorial discharge induced by the equatorial westerly current. In any case, I don't think we're having much issue generating more downwelling oceanic Kelvin Waves because another one has entered the fray as aforementioned, it will initially be met with destructive interference but when sub seasonal forcing realigns w/ the base state that's becoming more NINO like late in July and into August, this downwelling wave will likely intensify before reaching South America.

 

 

And does the +PMM actually aid the development of the niño, or is it largely a result of the low frequency state of circulation that favors warm pool discharges?

 

I’m more convinced of the latter. Too much off-equator convection can actually interfere with El Niño development, in the canonical sense. Some of the most prolific +PMMs like 1980 and 2014 were very anemic in the ENSO department.

 

 

I've discussed this at length numerous times, but the answer is yes literature shows that the PMM in both NWP simulations and observations contributes to the triggering of about 2/3rds of all El Nino events, is vital to the seasonal phase locking of ENSO, and when coupled with the negative phase of the SPMM increases the probability of central pacific/modoki El Nino. This year's +PMM regime is bigger than any that has ever been observed during the satellite era and the subsurface warming is way stronger than either 1980 & 2014 ever were, being more on par w/ moderate El Ninos like 2009 & 2002, which suggests that the former years may not be an adequate comparison here. Not every +PMM event will trigger an El Nino, however the probability of an El Nino is likely significantly higher when its coupled w/ a -AMO. 1980 and 2014 actually featured near or above normal SSTAs in the tropical Atlantic by this point in the summer, this year's SST anomalies have been rivaling the coldest years of the last -AMO regime in the 1980s & 1990s. Why does a cold tropical Atlantic matter for ENSO? 

 

A colder Atlantic is certainly more favorable to El Nino for several reasons, cooler MDR SSTs means the easterly trades are stronger which favors air/mass more readily piling into South America, where a major anomalous upward branch of the Hadley Cell is juxtaposed during El Ninos, essentially meaning that a cold AMO superimposes itself to some extent onto the larger-scale NINO circulation. A colder Atlantic also means there's one less ocean basin that's competing for upward motion on the global scale, affording the Pacific a greater chance to steal the show per say. In addition, the cold phase of the AMO pulls the ITCZ in the Pacific equatorward, again favoring El Nino (Sung et al (2015)). A seiching mechanism related to the Atlantic Meridional Overturning Circulation has also been proposed but it's much more elusive.

 

Here's a few excerpts from literature I've sifted through in the past few months that provide verification of this cold AMO-NINO relationship.

 

"The results show that the tropical Atlantic warming associated with the positive AMO phase leads to a

westward displacement of the Pacific Walker circulation and a cooling of the tropical Pacific Ocean, thereby

inducing anomalous descending motion over the central tropical Pacific. The descending motion then

excites a stationary Rossby wave pattern that extends northward to produce a nearly barotropic anticyclone

over the North Pacific."

https://www.ess.uci.edu/~yu/PDF/Lyu-Yu-Paek.JCLI.2017.pdf

 

"The long-lasting cold surface conditions of North Atlantic, i.e., the negative phase of Atlantic Multidecadal Oscillation (AMO), can intensify the El Niño–Southern Oscillation through the enhanced air-sea coupling under the increased central-to-eastern tropical Pacific mean sea surface temperature. However, the impact of warmer mean sea surface temperature (SST) is more efficient in the intensifying El Niño than La Niña, because of the nature of the exponential growth of atmospheric convection to SST change. Moreover, the farther eastward shift of the atmospheric convection during the negative AMO leads to the stronger El Niño due to the longer delayed negative feedback by oceanic waves. Therefore, the AMO mainly influences El Niño intensity rather than La Niña intensity."

 

"The SST anomalies in the El Niño years during AMO periods were stronger;"

 

"El Niño events were more significantly enhanced than La Niña events during AMO periods. The asymmetric development of the ENSO during the different AMO phases is related to thewarmer and wetter basic state of the central-to-eastern tropical Pacific, as shown in both the observations and the CM2.1 model output. Owing to the nonlinear properties in the SST-convection relationship, the warmer mean state of the SST in the central-to-eastern tropical Pacific enhances the sensitivity ofatmospheric convection to the same SST anomaly"

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2015GL064381

 

 

Also given this year's +PMM is the strongest and one of the longest lived events that's ever been observed, this only gives me more confidence that this +PMM will trigger an El Nino this year. 

 

 

You would be right that the current +PMM and -SPMM configuration does limit the maximum intensity of El Ninos especially in the canonical sense because the cold SE Pacific is a reflection of cumulative southern hemisphere mid-latitude RW activity and the trade wind anomalies in the subtropical SE Pacific propagate equatorward via WES feedback (described in Min (2015)) and affect the eastern portion of the equatorial basin only. However, the presence of this -SPMM doesn't limit the total probability of El Nino because it says nothing about the central Pacific and the dateline region which is in a favorable regime for warming right now. The base of the +PMM connects to the equator near the dateline, favoring westerly wind anomalies near the edge of the warm pool, and on its own, favors central Pacific El Nino. Like its counter part in the southern hemisphere, these westerly wind anomalies in a +PMM propagate towards the equator ultimately favoring El Nino, and the net ekman transport induced by the west - southwesterly wind anomalies generated in a +PMM transport water towards the eastern boundary region and the equator closer to the dateline, again favoring El Nino. The PMM in a general sense acts as effective red background noise "energizing" low frequency variance in the tropics, thereby exciting ENSO (see Lorenzo et al (2015) linked below).

 

All of the above evidence, literature, and current observations suggest that a weak-moderate central Pacific El Nino is most likely in 2018-19. Furthermore, the observational record in addition to the expected intensity of this El Nino (if one were to form) also argue that the probability of another El Nino in 2019-20 is higher than long-term average (~30-33%).

 

To close this post I'll reiterate that according to the ENS ONI, since 1865, 50-60% of first year-weak moderate El Ninos are followed immediately by another El Nino. In about 85% of those cases where another El Nino occurred in the following year, the 2nd El Nino was stronger than the first one. Keep this in mind going forward.

 

 

There's lots of literature on this topic, I'm only showing a few pieces I've read through.

 

 

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2007GL030302

 

https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-16-0063.1

 

https://journals.ametsoc.org/doi/pdf/10.1175/2008JCLI2473.1

 

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2015GL066281

 

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/grl.50571

 

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2001GL013435

 

 

"The majority of ENSO events in both nature and the coupled model are preceded by MM events."

[Webberweather53]

If you compare the subsurface temperature anomalies to years like 2012, last year, 2014 wherein a significant NINO (or in the case of 2014 strong NINO) head fake occurred, we're blowing them out of the water (no pun intended ) with exception to 2012.

 

2012 is an interesting case study because neither a +PMM or cold Atlantic were present during the summer of 2012, and furthermore most of the intense +SSTAs were confined to the far EP unlike this year. The warm tropical Atlantic, -PMM, and where the greatest warming initiated in the Eq Pacific were tip offs of a NINO head fake in 2012. I use 2012 as a prime example w/ similar subsurface warming and a bgd climate to this year to showcase how the PMM and tropical Atlantic as I discussed above are important in determining ENSO evolution. I believe based on observations & literature (some of which I linked above) that they provide valid, easy to recognize clues wrt forthcoming ENSO behavior and are reliable warning signs of either impending El Ninos or head fakes, 2012 just solidifies this rationale.

 

This year however couldn't be more different atm from 2012 outside of the subsurface and is following the recipe of success w/ a cold Atlantic, +PMM, and initiating in the Central Pacific, I'll explain why the latter is important below.

 

 

 

 

 

 

 

If you also were to analyze the early evolution of all these head fakes, they all observed vigorous eastern Pacific warming early on in their lifetimes, whereas this year seems to be following a completely different path with the most intense +SSTAs based in the central Pacific. We know that the climatological SSTs near the dateline are closer to the threshold necessary to readily generate convection. The implications of this are that weak events based in the CP like this year instead of the EP (as was the case initially in 2012, 2014,  & 2017) are more likely to generate convective feedback that non-linearly reinforces and grows the pre-existing SST anomaly. What this may also mean is that pound for pound, the North Pacific Meridional Mode may be a more effective generator of El Nino than the SPMM and having a +NPMM/-SPMM is more favorable than -NPMM/+SPMM because the base of the NPMM is directly connected to the edge of the warm pool whereas the SPMM is confined to the eastern Eq Pacific, limiting its potential for non-linear feedback unless a strong or extraordinary El Nino like 1982, 1997, &/or 2015 is observed.

[OKwx2k4]

Thank you for the great write ups and for sharing information. Both incredibly impressive and fascinating.

[Phil]

I see where you're coming from but the latter isn't true either. When a Kelvin wave reflects onto a boundary it returns as a rossby wave of the same sign. Meaning that these downwelling Rossby Waves created by reflection of the KW at the eastern boundary also suppress the thermocline. What actually enhances near-equatorial upwelling during El Nino events is the westward flowing surface currents which are in the same sense as earth's rotation generating cyclonic wind stress curl anomalies that augment Sverdrup transport, in effect increasing poleward export of water from the equator. Those westward propagating off-equatorial Rossby Waves actually do contribute to some extent to retaining heat in the Eq Pacific because their westward propagation contributes to anticyclonic wind stress curl that offsets the Equatorial discharge induced by the equatorial westerly current. In any case, I don't think we're having much issue generating more downwelling oceanic Kelvin Waves because another one has entered the fray as aforementioned, it will initially be met with destructive interference but when sub seasonal forcing realigns w/ the base state that's becoming more NINO like late in July and into August, this downwelling wave will likely intensify before reaching South America.

But ERW’s suppress the thermocline poleward of the equator rather than along it...without follow-up downwelling OKW activity, how can you conserve mass and momentum after an OKW diffracts into an ERW without a relative cessation of equatorial downwelling (in the absence of follow-up OKW activity)?

 

There would have to be another OKW to continue modulating the shoaling of the thermocline after the first ERW transition, no?

 

I've discussed this at length numerous times, but the answer is yes literature shows that the PMM in both NWP simulations and observations contributes to the triggering of about 2/3rds of all El Nino events, is vital to the seasonal phase locking of ENSO, and when coupled with the negative phase of the SPMM increases the probability of central pacific/modoki El Nino. This year's +PMM regime is bigger than any that has ever been observed during the satellite era and the subsurface warming is way stronger than either 1980 & 2014 ever were, being more on par w/ moderate El Ninos like 2009 & 2002, which suggests that the former years may not be an adequate comparison here.

Fascinating stuff man. I’ve read contradicting literature on this, however. Because a +PMM is largely a result of a weaker and/or poleward displacement of the NPAC high, which is indicative of stunted Indo-Pacific exhaust and a narrower longitudinal component of the Walker Cell, which would already favor WWBs/warm pool discharges to begin with under said state of transfer.

 

The +PMM can’t just manifest on its own accord..it has to be triggered by something. IE, it’s technically a result of the same warm pool/convective dynamics that play a role in modulating ENSO/thermocline shoaling in the first place.

 

I think it’s safe to say the process begins with changes to circulo-convective modes, initiated peripherally, which modulate the boundary conditions governing of the structural evolution of the west-Pacific warm pool.

 

I’d argue (and there is literature to substantiate this as well) that the +PMM is more of a positive/constructive feedback to a westward dislocation of the warm pool itself which aids the efficiency of discharge, rather than a dominant forcing on its own, unless it’s an overwhelmingly anomalous signature with a clear sign in the OHC/off-eq thermocline.

 

FWIW, as with most +PMMs, the signature becomes quite shallow in the presence of OKWs..barely even reflects in the anomalies right now. So it’s easily subject to intraseasonal disruption..IE it’s sustained by supportive peripheral boundary conditions.

 

http://www.cpc.ncep.noaa.gov/products/GODAS/ocean_briefing_new/mnth_hc_hcdiff_glb_xy.gif

 

Not every +PMM event will trigger an El Nino, however the probability of an El Nino is likely significantly higher when its coupled w/ a -AMO. 1980 and 2014 actually featured near or above normal SSTAs in the tropical Atlantic by this point in the summer, this year's SST anomalies have been rivaling the coldest years of the last -AMO regime in the 1980s & 1990s. Why does a cold tropical Atlantic matter for ENSO?

 

A colder Atlantic is certainly more favorable to El Nino for several reasons, cooler MDR SSTs means the easterly trades are stronger which favors air/mass more readily piling into South America, where a major anomalous upward branch of the Hadley Cell is juxtaposed during El Ninos, essentially meaning that a cold AMO superimposes itself to some extent onto the larger-scale NINO circulation. A colder Atlantic also means there's one less ocean basin that's competing for upward motion on the global scale, affording the Pacific a greater chance to steal the show per say. In addition, the cold phase of the AMO pulls the ITCZ in the Pacific equatorward, again favoring El Nino (Sung et al (2015)).

That’s certainly fascinating, but I’m having trouble connecting with what you’re predicting.

 

The +PMM does the opposite of the -AMO/-AMM, and displaces/broadens the Pacific ITCZ poleward east of 150W. And if both the Atlantic and the equatorial EPAC are cold, and there’s subsidence centered over South America as a result, trades in the EPAC along/east of 120W would be stronger, all else being equal, no? And the zonal SSTA gradient across the Pacific should be stronger as well.

 

So it’s no surprise that the recent Atlantic SSTA warming occurred in conjunction with stronger westerlies developing over the EPAC. There was an earlier CCKW passage that aided lift/divergence aloft across the EPAC domain.

 

This post is getting too long for my phone, so I’ll have to respond to the rest of the literature you sited in a followup post. But thank you for the fantastic reading and analysis..I really do enjoy these discussions.

[Black Hole]

If you compare the subsurface temperature anomalies to years like 2012, last year, 2014 wherein a significant NINO (or in the case of 2014 strong NINO) head fake occurred, we're blowing them out of the water (no pun intended ) with exception to 2012.

 

2012 is an interesting case study because neither a +PMM or cold Atlantic were present during the summer of 2012, and furthermore most of the intense +SSTAs were confined to the far EP unlike this year. The warm tropical Atlantic, -PMM, and where the greatest warming initiated in the Eq Pacific were tip offs of a NINO head fake in 2012. I use 2012 as a prime example w/ similar subsurface warming and a bgd climate to this year to showcase how the PMM and tropical Atlantic as I discussed above are important in determining ENSO evolution. I believe based on observations & literature (some of which I linked above) that they provide valid, easy to recognize clues wrt forthcoming ENSO behavior and are reliable warning signs of either impending El Ninos or head fakes, 2012 just solidifies this rationale.

 

This year however couldn't be more different atm from 2012 outside of the subsurface and is following the recipe of success w/ a cold Atlantic, +PMM, and initiating in the Central Pacific, I'll explain why the latter is important below.

 

 

 

 

If you also were to analyze the early evolution of all these head fakes, they all observed vigorous eastern Pacific warming early on in their lifetimes, whereas this year seems to be following a completely different path with the most intense +SSTAs based in the central Pacific. We know that the climatological SSTs near the dateline are closer to the threshold necessary to readily generate convection. The implications of this are that weak events based in the CP like this year instead of the EP (as was the case initially in 2012, 2014,  & 2017) are more likely to generate convective feedback that non-linearly reinforces and grows the pre-existing SST anomaly. What this may also mean is that pound for pound, the North Pacific Meridional Mode may be a more effective generator of El Nino than the SPMM and having a +NPMM/-SPMM is more favorable than -NPMM/+SPMM because the base of the NPMM is directly connected to the edge of the warm pool whereas the SPMM is confined to the eastern Eq Pacific, limiting its potential for non-linear feedback unless a strong or extraordinary El Nino like 1982, 1997, &/or 2015 is observed.

 

Appreciate your thoughts and time writing this and other posts.

 

In this and the previous post you talk about +PMM, and then I assume this is divided into NPMM and SPMM in your quoted post. I have a general sense about these from context, but can you define these in terms of SST anomalies (or otherwise) for me. I want to have a better sense of what you are getting at.

 

El nino modoki tends to be associated with warmer and drier winters in the Great Basin region where i live, from what I have seen anyway. Any early thoughts on that? I think el nino modoki often is associated with an enhanced monsoon season in the SW. Hopefully we see that this year.  

[Webberweather53]

But ERW’s suppress the thermocline poleward of the equator...without follow-up downwelling OKW activity, how can you conserve mass and momentum after an OKW diffracts into an ERW without a relative cessation of equatorial downwelling (in the absence of follow-up OKW activity)?

 

There would have to be another OKW to continue modulating the shoaling of the thermocline after the first ERW, no?

 

 

Interesting stuff man. I’ve read contradicting literature on this, however. Because a +PMM is largely a result of a weaker and/or more poleward NPAC high, which is indicative of stunted Indo-Pacific exhaust and a narrower Walker Cell, which would already favor WWBs/warm pool discharges to begin with.

 

The +PMM can’t just manifest on its own accord..it has to be triggered by something. IE, it’s trchnically a result of the same warm pool/convective dynamics that play a role in modulating ENSO/thermocline shoaling in the first place.

 

So I’d argue it’s more of a positive/constructive feedback than a dominant forcing unless it’s an overwhelmingly anomalous signature with a clear sign in the OHC/off-eq thermocline.

 

FWIW, as with most +PMMs, the signature becomes quite shallow in the presence of OKWs..barely even reflects in the anomalies right now. So it’s easily subject to intraseasonal disruption..IE it’s sustained by supportive peripheral boundary conditions.

 

http://www.cpc.ncep.noaa.gov/products/GODAS/ocean_briefing_new/mnth_hc_hcdiff_glb_xy.gif

 

 

That’s certainly interesting, but a +PMM does the opposite, and displaces/broadens the Pacific ITCZ poleward east of 150W. And if both the Atlantic and the equatorial EPAC are cold, and there’s subsidence centered over South America as a result, trades in the EPAC along/east of 120W would be stronger, all else being equal, no? And the zonal SSTA gradient across the Pacific should be stronger.

 

So it’s no surprise that the recent Atlantic SSTA warming occurred in conjunction with stronger westerlies developing over the EPAC. There was an earlier CCKW passage that aided lift/divergence aloft across the EPAC domain.

 

This post is getting too long for my phone, so I’ll have to respond to the rest of the literature you sited in a followup post. But thank you for the fantastic reading and analysis..I really do enjoy these discussions.

 

The EQ RWs suppress the thermocline most appreciably a few degrees from the equator but to reiterate once again, because of the anticyclonic wind stress curl generated from the westward current associated w/ these waves, it actually offsets the anomalous discharge promoted by an eastward flowing equatorial current. This is an important connection to make because its related to the discharge-recharge hypothesis that explains why westward flowing currents and surface winds in La Nina charge the Eq Pacific w/ warm water and limit poleward discharge. Similarly westward propagating, slower moving Eq Rossby Waves generated by downwelling KW activity also offset the poleward discharge during NINOs which is a crucial mechanism that terminates them. There's lots of literature on this topic.

 

As far as the PMM is concerned, you're really getting into a chicken-egg argument here. Again the PMM is generated by cumulative mid-latitude RW activity in the preceding winter that leaves a seasonal footprint which persists into the following spring. The depth of the anomalous warming associated w/ a PMM isn't as important as the surface reflection which affects low-level trades in the central and NE subtropical Pacific, you can easily have instances where it doesn't extend to an appreciable depth yet still yields similar forcing, additionally the mixed layer isn't that deep at this time of the year there barring the occasional TC so it likely won't matter all that much. The tropical forcing component from the warm pool is only one component to that RW activity which creates the PMM. The ITCZ is pushed poleward of its climatological position only in the eastern Pacific during +PMM, whereas because the base of the PMM extends directly onto the equator in the central Pacific the ITCZ actually remains close to the equator near the edge of the warmpool where non-linear feedbacks can take over and reinforce the SST anomaly and remotely force +SSTAs in the EP thru WWBs. (remote SST forcing component is larger than the local piece in the EP). The ITCZ juxtaposition in the Eastern Pacific doesn't matter as much because non-linear convective feedbacks don't occur here except in the strongest El Ninos, this is exactly why most weak EP-based NINOs in the modern era have failed as stated earlier.

[Webberweather53]

Appreciate your thoughts and time writing this and other posts.

 

In this and the previous post you talk about +PMM, and then I assume this is divided into NPMM and SPMM in your quoted post. I have a general sense about these from context, but can you define these in terms of SST anomalies (or otherwise) for me. I want to have a better sense of what you are getting at.

 

El nino modoki tends to be associated with warmer and drier winters in the Great Basin region where i live, from what I have seen anyway. Any early thoughts on that? I think el nino modoki often is associated with an enhanced monsoon season in the SW. Hopefully we see that this year.  

 

Sure thing. Yeah when I refer to +PMM it's usually the North Pacific Meridional Mode (NPMM) because this was first recognized by Chang and Vimont and likely plays a more prominent role in determining total ENSO probability. There are several reasons to believe if an El Nino occurs this year it'll be central pacific based/modoki. Namely...

A: Since 1976 almost every (successful) El Nino has started in the central Pacific

 

B: +NPMM/-SPMM configuration we have right now w/ warm water in the tropical and subtropical North Pacific (+PMM), and cold water in the SE Pacific (-SPMM) has been to shown to favor modoki over canoncial/classical El Nino.

See Min (2015) for more on this: https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-16-0063.1

 

C: ENSO flavor is moderately related to intensity. Weak-moderate El Ninos like we're expecting this year are more likely to be modoki/CP-based than Strong-Super events (obviously we know this isn't always the case however).

[Webberweather53]

As noted earlier this year and 2012 are on virtually equal footing w/ subsurface temperature anomalies in the Equatorial Pacific but couldn't be farther apart in the subtropical Northeast-central Pacific, tropical Atlantic, and how the El Nino events initially evolved. 2012-13 faded all the way deep into cold neutral conditions by the winter but will this year follow suit? The literature and observations noted above argue otherwise that this won't be a head fake.

 

2012

http://www.bom.gov.au/archive/oceanography/ocean_anals/IDYOC002/IDYOC002.201207.gif

 

 

http://www.bom.gov.au/archive/oceanography/ocean_anals/IDYOC002/IDYOC002.201807.gif

 

 

If you still don't buy into what I'm saying above w/ the PMM & tropical Atlantic influencing ENSO that's fine, we'll have the luxury of watching this idealized experiment take place w/ the same subsurface look being initialized in the Eq Pacific but vastly different boundary conditions in the subtropical North Pacific and tropical Atlantic, all without having to use a climate model!

[Phil]

If you compare the subsurface temperature anomalies to years like 2012, last year, 2014 wherein a significant NINO (or in the case of 2014 strong NINO) head fake occurred, we're blowing them out of the water (no pun intended ) with exception to 2012.

 

2012 is an interesting case study because neither a +PMM or cold Atlantic were present during the summer of 2012, and furthermore most of the intense +SSTAs were confined to the far EP unlike this year. The warm tropical Atlantic, -PMM, and where the greatest warming initiated in the Eq Pacific were tip offs of a NINO head fake in 2012. I use 2012 as a prime example w/ similar subsurface warming and a bgd climate to this year to showcase how the PMM and tropical Atlantic as I discussed above are important in determining ENSO evolution. I believe based on observations & literature (some of which I linked above) that they provide valid, easy to recognize clues wrt forthcoming ENSO behavior and are reliable warning signs of either impending El Ninos or head fakes, 2012 just solidifies this rationale.

 

This year however couldn't be more different atm from 2012 outside of the subsurface and is following the recipe of success w/ a cold Atlantic, +PMM, and initiating in the Central Pacific, I'll explain why the latter is important below.

 

 

If you also were to analyze the early evolution of all these head fakes, they all observed vigorous eastern Pacific warming early on in their lifetimes, whereas this year seems to be following a completely different path with the most intense +SSTAs based in the central Pacific. We know that the climatological SSTs near the dateline are closer to the threshold necessary to readily generate convection. The implications of this are that weak events based in the CP like this year instead of the EP (as was the case initially in 2012, 2014, & 2017) are more likely to generate convective feedback that non-linearly reinforces and grows the pre-existing SST anomaly. What this may also mean is that pound for pound, the North Pacific Meridional Mode may be a more effective generator of El Nino than the SPMM and having a +NPMM/-SPMM is more favorable than -NPMM/+SPMM because the base of the NPMM is directly connected to the edge of the warm pool whereas the SPMM is confined to the eastern Eq Pacific, limiting its potential for non-linear feedback unless a strong or extraordinary El Nino like 1982, 1997, &/or 2015 is observed.

But the reason canonical niño attempts tend to fail nowadays is a result of the presently unfavorable seasonality of the AMM (WHEM-ITCZ/z-cell network) which favors the more modoki style evolution via westward shift of ambient WP exhaust.

 

But modoki-type evolutions don’t rely as much on constructive interference from the PMM when compared to the canonical type evolutions. In modoki style years during the present cycle of AMM seasonality (2009, 2006, 2004, 2002, etc) the strongest niños (2009, 2002, etc) tended to have lower PMMs, while the weakest niños (2004, 2007, etc) tended to have higher PMMs.

 

Which makes theoretical sense to me, with the AMM tending to trend positive into boreal autumn in conjunction with the seasonal equatorward movement of the Pacific ITCZ away from those +PMM waters favoring weaker EPAC convection relative to WPAC convection.

[Phil]

The EQ RWs suppress the thermocline most appreciably a few degrees from the equator but to reiterate once again, because of the anticyclonic wind stress curl generated from the westward current associated w/ these waves, it actually offsets the anomalous discharge promoted by an eastward flowing equatorial current. This is an important connection to make because its related to the discharge-recharge hypothesis that explains why westward flowing currents and surface winds in La Nina charge the Eq Pacific w/ warm water and limit poleward discharge. Similarly westward propagating, slower moving Eq Rossby Waves generated by downwelling KW activity also offset the poleward discharge during NINOs which is a crucial mechanism that terminates them. There's lots of literature on this topic.

Except that assumes a relatively balanced bihemispheric diffraction of the OKW into ERWs (which often isn’t the case under anomalous MM regimes) and the stresses in question are only present underneath the ERW trail itself, not the entire basin (in the absence of additional OKW activity).

 

And either way, it’s still not structurally comparable to the state of transfer under the initial downwelling OKW, where off-equator water mass is falling equatorward, which is not true to the same extent after the formation of the ERW(s).

 

Not to mention any potential constructive/destructive interference from peripheral forcings on atmospheric circulation. These events all evolve uniquely (to state the obvious). If they didn’t, predicting ENSO would be a cakewalk.

 

As far as the PMM is concerned, you're really getting into a chicken-egg argument here. Again the PMM is generated by cumulative mid-latitude RW activity in the preceding winter that leaves a seasonal footprint which persists into the following spring. The depth of the anomalous warming associated w/ a PMM isn't as important as the surface reflection which affects low-level trades in the central and NE subtropical Pacific, you can easily have instances where it doesn't extend to an appreciable depth yet still yields similar forcing, additionally the mixed layer isn't that deep at this time of the year there barring the occasional TC so it likely won't matter all that much. The tropical forcing component from the warm pool is only one component to that RW activity which creates the PMM.

I agree re: equatorward cyclonic breakers aiding in the generation the PMM signature, but the extent to which occurs and sustains depends on a reduction in subtropical NH trades/poleward-displaced NPAC high. The +PMM could not occur without it. And the those boundary conditions are all produced by peripherally-initiated and/or nonlinear regional dynamics that modulate the ventilation of the warm pool.

 

I’m personally not aware of any +PMM trigger that doesn’t run through the Indo-Pacific warm pool first. If you know of any, I’d be very interested in learning about them.

 

The ITCZ is pushed poleward of its climatological position only in the eastern Pacific during +PMM, whereas because the base of the PMM extends directly onto the equator in the central Pacific the ITCZ actually remains close to the equator near the edge of the warmpool where non-linear feedbacks can take over and reinforce the SST anomaly and remotely force +SSTAs in the EP thru WWBs. (remote SST forcing component is larger than the local piece in the EP). The ITCZ juxtaposition in the Eastern Pacific doesn't matter as much because non-linear convective feedbacks don't occur here except in the strongest El Ninos, this is exactly why most weak EP-based NINOs in the modern era have failed as stated earlier.

But since we’re in a climate regime of post-solstice AMM increases (tied to changes in WP exhaust and other climate changes), in conjunction w/ the +PMM, it should become increasingly hostile to +ENSO as the ITCZ tries to migrate equatorward thru boreal autumn, as there’s an increasing off-equator component to the convention between 150W to 40W.

[Phil]

Just so there’s no misunderstanding, I’m not expecting a collapse to cold neutral like 2012/13.

 

I think we’ll see the weak niño head fake during the second half of summer into early autumn (in terms of ONI) with a return to neutral or warm neutral during the late autumn and winter.

[Webberweather53]

But the reason canonical niño attempts tend to fail nowadays is a result of the presently unfavorable seasonality of the AMM (WHEM-ITCZ/z-cell network) which favors the more modoki style evolution via westward shift of ambient WP exhaust.

 

But modoki-type evolutions don’t rely as much on constructive interference from the PMM when compared to the canonical type evolutions. In modoki style years during the present cycle of AMM seasonality (2009, 2006, 2004, 2002, etc) the strongest niños (2009, 2002, etc) tended to have lower PMMs, while the weakest niños (2004, 2007, etc) tended to have higher PMMs.

 

Which makes theoretical sense to me, with the AMM tending to trend positive into boreal autumn in conjunction with the seasonal equatorward movement of the Pacific ITCZ away from those +PMM waters favoring weaker EPAC convection relative to WPAC convection.

 

 

Not necessarily, this year's AMM set the bar lower than it ever has been, tanking to new record lows this past month (and almost for any month for that matter), we're not living in the 1995-2012 regime anymore for the time being so the first argument seems irrelevant.

 

This second statement doesn't make any sense whatsoever. If you actually read through the literature I've linked earlier you'd find that modoki evolutions actually do rely more on the PMM compared to canonical events because the north pacific meridional mode only significantly affects equatorial variability in the central Pacific because the base of the NPMM crosses the Eq Pacific near the dateline. The NPMM actually has little impact on the EP SST evolution and canonical events, this is reserved for the SPMM. Again, read the literature I sent you (please)...

 

The first bolded statement is true mainly because it's simply harder to generate higher SSTAs when the Equatorial Pacific is already stupid warm in a stronger event, obviously 2015-16 is a monstrous outlier that needs to be given due consideration.

The AMM really can't get any lower than it is now, a positive trend into this autumn (even a significant one) from where we stand now would still leave us with a very significant negative regime that's still not hostile to +ENSO.

 

 

Except that assumes a relatively balanced bihemispheric diffraction of the OKW into ERWs (which often isn’t the case under anomalous MM regimes) and the stresses in question are only present underneath the ERW trail itself, not the entire basin (in the absence of additional OKW activity).

 

And either way, it’s still not structurally comparable to the state of transfer under the initial downwelling OKW, where off-equator water mass is falling equatorward, which is not true to the same extent after the formation of the ERW(s).

 

Not to mention any potential constructive/destructive interference from peripheral forcings on atmospheric circulation. These events all evolve uniquely (to state the obvious). If they didn’t, predicting ENSO would be a cakewalk.

 

 

I agree re: equatorward cyclonic breakers aiding in the generation the PMM signature, but the extent to which occurs and sustains depends on a reduction in subtropical NH trades/poleward-displaced NPAC high. The +PMM could not occur without it. And the those boundary conditions are all produced by peripherally-initiated and/or nonlinear regional dynamics that modulate the ventilation of the warm pool.

 

I’m personally not aware of any +PMM trigger that doesn’t run through the Indo-Pacific warm pool first. If you know of any, I’d be very interested in learning about them.

 

 

But since we’re in a climate regime of post-solstice AMM increases (tied to changes in WP exhaust and other climate changes), in conjunction w/ the +PMM, it should become increasingly hostile to +ENSO as the ITCZ tries to migrate equatorward thru boreal autumn, as there’s an increasing off-equator component to the convention between 150W to 40W.

 

 

No it doesn't... The stresses actually become do become nearly basin wide in cases like this where one Kelvin Wave after the other is impinging on the eastern boundary region and reflecting into downwelling Rossby Wave. Rossby Wave wavelengths and slower phase speeds allow for much higher wavenumbers w/ Eq RWs, creating more or less traffic jams in the off-equatorial Pacific esp when compared to Kelvin Waves. Unless you're going to complete dismantle Sverdrup theory, none of this negates the fact that these RWs significantly hinder enhanced equatorial discharge associated w/ positive wind stress curl induced by the equatorial westerly wind anomalies.

 

This seems to be a common misconception amongst many tropical gurus, forcing is not a one way street, the mid-latitudes and tropics evolve together (Paul Roundy has done a lot of working on this) which means  everything will NOT go thru the Indo-WP warm pool and vis versa in the mid-latitudes. It's certainly an important player and arguably the most important globally but intrinsic mid-latitude variability and external forcing that's selectively expressed by the polar region are good examples wherein the forcing doesn't go thru the warm pool. You want an example, fine how about a +NAM forced in part externally via a major solar proton event that destroys a ton of ozone, cooling the polar stratosphere, ultimately favoring poleward circumglobal, poleward anticyclones as the stratospheric height and temperature anomalies descend into the troposphere w/ one of the major AO poles in the far NP, this would in essence favor stronger and potentially poleward displaced Aleutian ridging.

 

The problem with the last statement is this did not happen this year w/ the AMM, if anything the opposite has occurred and the AMM has tanked to new record lows since the last solstice, maybe next year a large-scale change may be afoot. The overwhelming majority of the ENSO convective footprint is west of 150W, I still don't see how that's going to matter here wrt total probability of an El Nino although again it will probably impact the strength and type of event we see which is what the literature shows.

 

Dan Vimont: "Wow - the AMM is the most negative it has ever been for June (-2.5 sigma for June), and the third most negative value since 1948. Meanwhile, the PMM is large and positive. The spatial SST structure is "as AMM as it gets"

 

https://twitter.com/DanVimont/status/1013878561353207809

[Webberweather53]

Just so there’s no misunderstanding, I’m not expecting a collapse to cold neutral like 2012/13.

 

I think we’ll see the weak niño head fake during the second half of summer into early autumn (in terms of ONI) with a return to neutral or warm neutral during the late autumn and winter.

 

Sorry but I have to strongly disagree with you. Unless the Atlantic warms up more than it ever has in the satellite era later this autumn to counteract the record low -AMM currently in place (good luck w/ that) and we see no additional sub seasonal help following the surge in NINO forcing late in July & August (also not terribly likely), I don't see this panning out. A weak-moderate modoki El Nino seems far more likely in 2018-19 w/ another NINO attempt potentially looming in 2019-20.

[Phil]

Not necessarily, this year's AMM set the bar lower than it ever has been, tanking to new record lows this past month (and almost for any month for that matter), we're not living in the 1995-2012 regime anymore for the time being so the first argument seems irrelevant.

 

This second statement doesn't make any sense whatsoever. If you actually read through the literature I've linked earlier you'd find that modoki evolutions actually do rely more on the PMM compared to canonical events because the north pacific meridional mode only significantly affects equatorial variability in the central Pacific because the base of the NPMM crosses the Eq Pacific near the dateline. The NPMM actually has little impact on the EP SST evolution and canonical events, this is reserved for the SPMM. Again, read the literature I sent you (please)...

Thanks for the response. I actually have read most the aforementioned literature. The difference is that I’ve elected to confine my reference period only to years after 1995, until it can be ascertained that the seasonality of the AMM/WHEM-ITCZ system has indeed changed.

 

This is what I’m referring to. Note the difference in the AMM/AMO sign in late summer/autumn vs spring. The seasonality is just as important as the sign itself in determining where the system state is headed. This ties right into the z-cell changes and failure of the more canonical niño progressions in recent decades.

 

 

As for the PMM, when isolating my base period to the period from 1995-present, there is actually a weak inverse correlation between the sign of the PMM and the ONI (during +ENSO years). Meanwhile, the opposite seems to be true in -ENSO years.

 

No it doesn't... The stresses actually become do become nearly basin wide in cases like this where one Kelvin Wave after the other is impinging on the eastern boundary region and reflecting into downwelling Rossby Wave.

This is what I was asking you yesterday with my aloof “backslosh” comment. So I take it you believe the weaker OKW near the dateline has enough inertia behind it to perpetuate the downwelling process east of 150W after the bigger OKW diffracts into its ERW cycle later this month?

 

That’s what I’m skeptical of, in the absence of WWB activity west of ~140W or so.

 

Rossby Wave wavelengths and slower phase speeds allow for much higher wavenumbers w/ Eq RWs, creating more or less traffic jams in the off-equatorial Pacific esp when compared to Kelvin Waves. Unless you're going to complete dismantle Sverdrup theory, none of this negates the fact that these RWs significantly hinder enhanced equatorial discharge associated w/ positive wind stress curl induced by the equatorial westerly wind anomalies.

As far as I’m aware, it’s the returning easterly zonal current that is “hindered” by the ERW mechanics. But you’re still evacuating water mass poleward from the equator during the diffraction process, which aids upwelling/vertical overturning in the absence of follow-up OKW activity.

 

This seems to be a common misconception amongst many tropical gurus, forcing is not a one way street, the mid-latitudes and tropics evolve together (Paul Roundy has done a lot of working on this) which means everything will NOT go thru the Indo-WP warm pool and vis versa in the mid-latitudes. It's certainly an important player and arguably the most important globally but intrinsic mid-latitude variability and external forcing that's selectively expressed by the polar region are good examples wherein the forcing doesn't go thru the warm pool. You want an example, fine how about a +NAM forced in part externally via a major solar proton event that destroys a ton of ozone, cooling the polar stratosphere, ultimately favoring poleward circumglobal, poleward anticyclones as the stratospheric height and temperature anomalies descend into the troposphere w/ one of the major AO poles in the far NP, this would in essence favor stronger and potentially poleward displaced Aleutian ridging.

Nice post here. So, I agree with you re: external forcings on the tropics (which includes the warm pool)..otherwise it’s very difficult (if not impossible) to explain some of the correlations between ENSO dynamics and solar forcing(s). Too much there to be a coincidence.

 

However, I’m only referring to the maintenance of a PMM signature. I think it’s obvious that the slew of external forcings (I can think of dozens) aiding the RWB/PMM structure do so via a lower frequency modulation of warm pool structure and ventilation at trigger points. There are obvious correlations between the structure of the warm pool and the PMM/AMM. Very coherent ones. There are a number of cases where the warm pool structure refused to give way and the PMM failed to reverse.

 

The problem with the last statement is this did not happen this year w/ the AMM, if anything the opposite has occurred and the AMM has tanked to new record lows since the last solstice, maybe next year a large-scale change may be afoot. The overwhelming majority of the ENSO convective footprint is west of 150W, I still don't see how that's going to matter here wrt total probability of an El Nino although again it will probably impact the strength and type of event we see which is what the literature shows.

If we fail to walk back towards neutral/positive AMM this year, then yeah, my ENSO forecast could bust. I’m betting on recent climo tendencies here..a reversal in this AMM tendency would be huge, and would definitely have climate consequences as well. So I’m not ready to throw my chips in yet.

[Phil]

[Webberweather53]

Thanks for the response. I actually have read most the aforementioned literature. The difference is that I’ve elected to confine my reference period only to years after 1995, until it can be ascertained that the seasonality of the AMM/WHEM-ITCZ system has indeed changed.

 

This is what I’m referring to. Note the difference in the AMM/AMO sign in late summer/autumn vs spring. The seasonality is just as important as the sign itself in determining where the system state is headed. This ties right into the z-cell changes and failure of the more canonical niño progressions in recent decades.

 

 

As for the PMM, when isolating my base period to the period from 1995-present, there is actually a weak inverse correlation between the sign of the PMM and the ONI (during +ENSO years). Meanwhile, the opposite seems to be true in -ENSO years.

 

 

This is what I was asking you yesterday with my aloof “backslosh” comment. So I take it you believe the weaker OKW near the dateline has enough inertia behind it to perpetuate the downwelling process east of 150W after the bigger OKW diffracts into its ERW cycle later this month?

 

That’s what I’m skeptical of, in the absence of WWB activity west of ~140W or so.

 

 

As far as I’m aware, it’s the returning easterly zonal current that is “hindered” by the ERW mechanics. But you’re still evacuating water mass poleward from the equator during the diffraction process, which aids upwelling/vertical overturning in the absence of follow-up OKW activity.

 

 

Nice post here. So, I agree with you re: external forcings on the tropics (which includes the warm pool)..otherwise it’s very difficult (if not impossible) to explain some of the correlations between ENSO dynamics and solar forcing(s). Too much there to be a coincidence.

 

However, I’m only referring to the maintenance of a PMM signature. I think it’s obvious that the slew of external forcings (I can think of dozens) aiding the RWB/PMM structure do so via a lower frequency modulation of warm pool structure and ventilation at trigger points. There are obvious correlations between the structure of the warm pool and the PMM/AMM. Very coherent ones. There are a number of cases where the warm pool structure refused to give way and the PMM failed to reverse.

 

 

If we fail to walk back towards neutral/positive AMM this year, then yeah, my ENSO forecast could bust. I’m betting on recent climo tendencies here..a reversal in this AMM tendency would be huge, and would definitely have climate consequences as well. So I’m not ready to throw my chips in yet.

 

No doubt there was a major step change in AMO-AMM behavior after 1995 but this year is a huge anomaly from just about everything we've seen since then w/ the latter (AMM) being in record low territory for crying out loud, I don't see this line of rationale being applicable here unless you firmly believe we're about to witness one of the most unreal turnarounds ever observed later this summer and autumn in the AMM/AMO. The downwelling KW crossing the CP will reinforce the already suppressed thermocline in the EP, even w/o it, we'd still have to contend w/ a warming Eq Pacific for the next 2-3 months at a minimum, even longer still for the central Pacific. I'm already seeing signs of low frequency coupling to the atmosphere & the next CCKW fixing to cross the Eq Pacific will be met with open arms.

 

http://blog.southernwx.com/wp-content/uploads/2018/07/chi200.cfs_.eqtr_.png

 

 

 

This seemingly weak downwelling wave has recently formed following the last round of intraseasonal forcing earlier this past month which didn't feature the classic, strong WWB, it's still in an area of the central-western Pacific where the thermocline slope is modest in comparison to further E (usually harder to generate subsurface anomalies as a result) and I stated before, I expect the next bout of sub seasonal forcing late in July into August to intensify this downwelling KW before it hits the eastern boundary region in September, so it probably won't look quite as weak down the road if we get a renewed slackening of the easterly trades which is usually all that's needed at this stage in the game for a weak-moderate El Nino.

 

 

I honestly don't see what's so bad about the cumulative U wind forcing over the Eq Pacific. Let me remind you that 2009 (shown below) had no significant dateline WWBs up to this point in time and still went on to produce a borderline strong El Nino w/ a very similar subsurface look to this year.

 

http://blog.southernwx.com/wp-content/uploads/2018/07/2606-a000-1500-a0c9-9457-afaf-7d0d-6ae5.184.0.10.56.png

 

 

 

Now look at this year, we just had a very sizable WWB east of the dateline earlier this month from this last round of sub seasonal forcing & we're still reeling from the big MJO event this past February that helped set this all into motion.

 

http://blog.southernwx.com/wp-content/uploads/2018/07/2606-a000-1500-a0c9-9457-afaf-7d0d-6ae5.184.0.11.53.png

 

2006-07 went onto produce a weak NINO event, no signs of let up w/ strong easterlies dominating right up to this point in July,

surely you have to believe this year wouldn't go onto produce an El Nino would it? Or better yet that we somehow aren't any worse off than either 2006-07 & 2009-10 in the WWB forcing department.

 

http://blog.southernwx.com/wp-content/uploads/2018/07/2606-a000-1500-a0c9-9457-afaf-7d0d-6ae5.184.0.10.34.png

 

 

2014-15 lots of nearly continuous WWB activity early reminiscent of extraordinary El Ninos, only a couple easterly trade bursts near the dateline was all it took to set this back to a weak event. The cumulative U wind forcing was impressive yet we ended up w/ a weaker El Nino than 2009-10 that observed incessant dateline easterlies thru the summer.

http://blog.southernwx.com/wp-content/uploads/2018/07/75.184.9.71.184.0.20.8.png

 

 

1994-95, you certainly wouldn't know by looking at U850 anomalies that a borderline weak-moderate El Nino was coming

http://blog.southernwx.com/wp-content/uploads/2018/07/2606-a000-1500-a0c9-9457-afaf-7d0d-6ae5.184.0.25.10.png

 

 

By now you should get my point. This year isn't doing anywhere near as bad you're claiming it to be wrt WWB forcing in the Eq Pacific so far esp when you compare it to other successful weak-moderate and even borderline strong El Ninos up to this point in time. October and beyond though is typically when most of these events pick up the pace and we would certainly need to see more sustained WWB activity but there's plenty of time for that to occur.

 

Yeah I was about to say, tbh your +PMM comments took me for a tailspin because it made it seem like you were really out of touch w/ reality here given the huge -AMM in place right now. 

 

"If we fail to walk back towards neutral/positive AMM this year, then yeah, my ENSO forecast could bust. I’m betting on recent climo tendencies here..a reversal in this AMM tendency would be huge, and would definitely have climate consequences as well. So I’m not ready to throw my chips in yet."

 

Wow, you're being conservative here to say the least wrt clinging to your initial forecast based on AMM evolution. Like Dan Vimont said, you really can't get more -AMM than this. If your NINO head fake is hinging on the AMM flipping around positive or even going neutral in just 2-3 months, I'm sorry but I don't know what to tell you other than you're probably screwed.

http://blog.southernwx.com/wp-content/uploads/2018/07/atl.gif

 

http://blog.southernwx.com/wp-content/uploads/2018/07/compday.T3WWula5eG.gif

[Phil]

No doubt there was a major step change in AMO-AMM behavior after 1995 but this year is a huge anomaly from just about everything we've seen since then w/ the latter (AMM) being in record low territory for crying out loud, I don't see this line of rationale being applicable here unless you firmly believe we're about to witness one of the most unreal turnarounds ever observed later this summer and autumn in the AMM/AMO.

Sorry for the late reply. Busy 4th for me.

 

This (1990s-present) seasonality in the AMM/AMO is a result of very large scale, inertia-loaded processes in the atmosphere-ocean system that would be very hard to reverse in just one year. Look at what happened back in 1989 for an example of the inception of this situation..if the atmospheric circulation (anticyclonic breaker train) that maintains the -AMM is killed off every summer/fall by changes to WP exhaust/z-cell climatology, then for all intents and purposes you lose the -AMM as a forcing until the termination of the Eurasian monsoonal trough.

 

We’re already beginning to see the peripherally forced seasonality in the WHEM circulation affect the AMM. Over the last month (7/3/18 relative to 6/3/18):

 

 

So despite the *present* sign (of (-)AMM), if you’re losing it to destructive off-domain interference, your system state isn’t a -AMM system state to begin with because the origin of spatial radiance is elsewhere.

 

The downwelling KW crossing the CP will reinforce the already suppressed thermocline in the EP, even w/o it, we'd still have to contend w/ a warming Eq Pacific for the next 2-3 months at a minimum, even longer still for the central Pacific. I'm already seeing signs of low frequency coupling to the atmosphere & the next CCKW fixing to cross the Eq Pacific will be met with open arms.

 

http://blog.southernwx.com/wp-content/uploads/2018/07/chi200.cfs_.eqtr_.png

 

This seemingly weak downwelling wave has recently formed following the last round of intraseasonal forcing earlier this past month which didn't feature the classic, strong WWB, it's still in an area of the central-western Pacific where the thermocline slope is modest in comparison to further E (usually harder to generate subsurface anomalies as a result) and I stated before, I expect the next bout of sub seasonal forcing late in July into August to intensify this downwelling KW before it hits the eastern boundary region in September, so it probably won't look quite as weak down the road if we get a renewed slackening of the easterly trades which is usually all that's needed at this stage in the game for a weak-moderate El Nino.

 

I honestly don't see what's so bad about the cumulative U wind forcing over the Eq Pacific. Let me remind you that 2009 (shown below) had no significant dateline WWBs up to this point in time and still went on to produce a borderline strong El Nino w/ a very similar subsurface look to this year.

 

http://blog.southernwx.com/wp-content/uploads/2018/07/2606-a000-1500-a0c9-9457-afaf-7d0d-6ae5.184.0.10.56.png

 

Now look at this year, we just had a very sizable WWB east of the dateline earlier this month from this last round of sub seasonal forcing & we're still reeling from the big MJO event this past February that helped set this all into motion.

 

http://blog.southernwx.com/wp-content/uploads/2018/07/2606-a000-1500-a0c9-9457-afaf-7d0d-6ae5.184.0.11.53.png

 

2006-07 went onto produce a weak NINO event, no signs of let up w/ strong easterlies dominating right up to this point in July,

surely you have to believe this year wouldn't go onto produce an El Nino would it? Or better yet that we somehow aren't any worse off than either 2006-07 & 2009-10 in the WWB forcing department.

 

http://blog.southernwx.com/wp-content/uploads/2018/07/2606-a000-1500-a0c9-9457-afaf-7d0d-6ae5.184.0.10.34.png

 

 

2014-15 lots of nearly continuous WWB activity early reminiscent of extraordinary El Ninos, only a couple easterly trade bursts near the dateline was all it took to set this back to a weak event. The cumulative U wind forcing was impressive yet we ended up w/ a weaker El Nino than 2009-10 that observed incessant dateline easterlies thru the summer.

http://blog.southernwx.com/wp-content/uploads/2018/07/75.184.9.71.184.0.20.8.png

 

1994-95, you certainly wouldn't know by looking at U850 anomalies that a borderline weak-moderate El Nino was coming

http://blog.southernwx.com/wp-content/uploads/2018/07/2606-a000-1500-a0c9-9457-afaf-7d0d-6ae5.184.0.25.10.png

 

By now you should get my point. This year isn't doing anywhere near as bad you're claiming it to be wrt WWB forcing in the Eq Pacific so far esp when you compare it to other successful weak-moderate and even borderline strong El Ninos up to this point in time. October and beyond though is typically when most of these events pick up the pace and we would certainly need to see more sustained WWB activity but there's plenty of time for that to occur.

 

Yeah I was about to say, tbh your +PMM comments took me for a tailspin because it made it seem like you were really out of touch w/ reality here given the huge -AMM in place right now.

 

"If we fail to walk back towards neutral/positive AMM this year, then yeah, my ENSO forecast could bust. I’m betting on recent climo tendencies here..a reversal in this AMM tendency would be huge, and would definitely have climate consequences as well. So I’m not ready to throw my chips in yet."

 

Wow, you're being conservative here to say the least wrt clinging to your initial forecast based on AMM evolution. Like Dan Vimont said, you really can't get more -AMM than this. If your NINO head fake is hinging on the AMM flipping around positive or even going neutral in just 2-3 months, I'm sorry but I don't know what to tell you other than you're probably screwed.

http://blog.southernwx.com/wp-content/uploads/2018/07/atl.gif

 

http://blog.southernwx.com/wp-content/uploads/2018/07/compday.T3WWula5eG.gif

A few points.

 

1) The CFSv2 (and the vast majority climate model guidance,, tbh) almost always over-estimates low-frequency coupling to projected SSTAs at the expense of intraseasonal variability. I pay zero attention to those VP/OLR model projections outside of ENSO/low-freq situations that are already established.

 

2) I care less about where the AMM/U-winds/etc are right now, as opposed to where they’re going, and why. In this case, why would I extrapolate from a -AMM/OKW state that lacks discernible constructive interference in the derivations? When the climatology of the circulatory seasonality for the last two decades vehemently opposes extrapolations from a static state, that’s a huge red flag in my book.

 

3) There is no niño without additional warm pool discharge/OKW activity prominent enough to overcome intraseasonal forcing and the inertia of the thermocline return (currently timed for early September in the absence of said additional OKW activity). Without it, you necessarily lose ground. Climate models projecting a low frequency coupling is typical for pseudo-emergent states with some structural homogeneity to their programmed climatological EOFs. The model projections don’t impress me at all, tbh.

[Phil]

Notice how the aforementioned El Niños of 1994, 2002, 2006, and 2009 occurred because of subsequent WWB activity along/west of the dateline after the summer solstice, hindering Indonesian throughflow.

 

And the tendency is always towards increasing WWB activity from boreal winter/spring to boreal autumn/winter, rather than the opposite.

 

 

This is a climatological bedrock of niño years during this multidecadal regime of seasonality that initiated during the 1990s/anti-canonical era.

[Phil]

Meanwhile, +PMM years that lose ground in ONI after the fall equinox (AKA “head fake” years) tend to feature the opposite tendency, with strong WWB activity during boreal winter/spring then a walk-back during summer/autumn.

 

For example, look at 2014. It was “technically” a niño, albeit barely (since it started from a more +ENSO background state) but it still lost ground during boreal winter, and SSTs fell below Niño threshold for a significant period of time.

 

This year reminds me of 2014, in the sense that we had the significant WWB activity in J/F/M, which extended to/beyond the dateline, followed by a retraction during the subsequent months.

 

Here is 2014:

 

 

And here is 2018 so far. These two years share the structural homogeneity for “head fake” events.