Webberweather
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Eric Webb
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The GFS might be a bit overdone but I think we could see a gigantic WWB near the dateline next week as an Equatorial Rossby Wave interferes w/ the lowpass ENSO signal. We're at that time of the year where ENSO is most receptive to high frequency noise like this, granted you can clearly see this isn't just fleeting noise anymore w/ the 3rd legitimate 150E-180E WWB in the past month.- 704 replies
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A second SSW is more in line with the expected timing from tropical forcing via Garfinkel, we usually see the stratosphere warm the most a week or two after a West Pacific MJO event.
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We're getting a 1-2 punch of polar stratospheric warming events in both the northern and southern hemispheres, with the southern hemisphere undergoing final warming. This will continue to favor an accelerated, hyperactive Brewer Dobson Circulation with anomalous upwelling in the tropical stratosphere that favors enhanced tropical convection dominated by westward propagating convectively coupled waves in the warm pool. The southern hemisphere final warming event appears to be one of the catalysts for the observed change in equatorial wave spectra I'll discuss below with the northern hemisphere warming acting to further invigorate the MJO and contribute to its deceleration over the Maritime Continent. Notice how the southern hemisphere final warming event that began about 25-30 days ago directly coincides with when the MJO started to gain significant amplitude over the Indian Ocean in early December. This also marked the first point in the winter season where we finally broke this monotonous, Kelvin-Wave dominated 30 ish day periodicity to subseasonal tropical forcing. This is not a coincidence.
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"it's quite mind-boggling to read unequivocal, unqualified, dogmatic statements such as, "you're wrong," as if the putative final word has been uttered." Let's get a few things straight... You stated on multiple occasions that there was excess westerly momentum in the long-term signal in the subtropics, I dismantled this proposal multiple times. First the SST composite I responded to you with was supposedly indicative of +AAM in the subtropics. "This, in my view, corroborates the notion that zonal wind anomalies, off-equator, would be enhanced via strengthening meridional thermal gradients, and by extension, provide additional momentum injection into the atmosphere. " Then of course, this same composite you referred to had -AAM in the same locations you assumed it would be positive. Oops... Then you then went onto claim that I was somehow cherry picking the data and should use post 1976 NINOs to compare with that apparently showed excess subtropical +AAM. "Eric, you're comparing apples to oranges with those years ranges." "Note the stronger zonal winds in the sub-tropical belt 30 N reflected by the oranges, redolent of the fact that recent El Ninos have seen an increase in sub-tropical zonal winds and thus likely AAM compared to older years." Yet, once again you were wrong in this regard because there was -AAM in the NCEP R1 means ~20-30N in the difference composite. There's nothing dogmatic or unqualified about this, in fact I was looking at the EXACT same data you were. The biggest difference is unlike what you did, I didn't just eyeball the composites and assume my opinion was right based on that highly subjective analysis. The actual data doesn't lie and shows that there's -AAM (in blue) in the subtropics in those same NINOs you said had +AAM, that is a fact, there is no debate on this particular point even though you're trying to make it look like there is. In spite of how much you decided to wrongfully/childishly frame my responses to you as "unqualified" or "dogmatic" , it's an undeniable fact that your interpretations up to this point in time have been quite frankly wrong, whether you actually want to admit that or not is another story. It's truly "mind-boggling" how someone could be so wrong especially with basic interpretations like these yet fail to realize what's been starting them in the face the entire time. That's aside from the fact that this discussion was pretty civil and intellectually stimulating up until this point when you decided to instigate in nonsensical attacks like these. This is the last I'm going to say on this matter.
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"Note the stronger zonal winds in the sub-tropical belt 30 N reflected by the oranges" Once again, your interpretation is just flat-out wrong if you actually more closely inspected the data. Latitudinal averages of the zonal mean wind anomalies show anomalous easterlies in the subtropics ~20-30N in modern El Ninos. I recommend using cross-section analyses in NCEP R1, looks can be deceiving from standard difference plots.
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This isn't an apples-oranges comparison, I chose to keep my years within the satellite era because upper tropospheric data can be pretty sketchy before the mid-late 1970s, but in any case it's pretty obvious that your interpretation of the corresponding SST composite couldn't have been any further from reality! Btw, if you're trying to detect a base state change in AAM due to the background climate, it would be more pertinent to include all years instead of El Ninos only so as to limit internal variability and sampling issues. Your above composite if anything is actually an apples-oranges comparison! You need to be aware of the fact that 3 of the 4 strongest El Ninos since 1950 occurred in the first group your subtracting from (1982-83, 1997-98, & 2015-16) and they're likely heavily skewing the results in your composite to show +AAM ~30-40N & thus the set of years you're subtracting from has significantly stronger El Ninos in it. If your goal was to showcase base state changes in a particular ENSO phase from observations, good luck with that because internal variability is too large for an analysis like this until the sample size of events for both groups exceeds 30-40 (& this isn't simply determined from basic statistics, several papers have also noted this to be a sufficient sample size s.t. ENSO signals become larger than internal varaibility, Garfinkel has some nice work on this topic). The above composite doesn't line up with this year either, notice how the +AAM is poleward of 30N whereas this year it's been below this latitude. That seems trivial superficially but it actually matters a lot here considering that the half-width of the concomitant circulation anomalies are on the order of the difference between these "modern" Ninos and this year. What you're showing only supports my earlier claims, and it's a reflection of similar base state response towards Hadley Cell expansion in fact! Only difference is the HC contracts more in El Nino years due to angular momentum deposition at the equatorward flank of the waveguide so the excess westerly momentum is still poleward of canonical NINO, but migrating poleward at a lower latitude than it would in La Ninas. It also really doesn't matter what start & end year I chose for my composite, there's a definitive long-term trend towards subtropical -AAM esp ~30N after the 1997-98 super NINO, which is completely different from what we're seeing this year. In fact, what we're seeing now is a temporary throwback to a cooler base state climate w/ contracted HC thus subtropical +AAM would be expected with tropical warming and subtropical cooling, if anything. Here, I've blown up the original AAM time series plot and clearly marked the post 1997-98 subtropical -AAM that's corresponded with the aforementioned warming in the subtropics which completely flies in the face of what you've been trying to claim.
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Absolutely classic wave-1 displacement/Sudden Stratospheric Warming Event precursor in the extended as AAM propagates poleward in response to the recent significant bout of tropical forcing.
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Furthermore, you also need to account for where this subtropical warming is occurring in relation to the waveguide because it doesn't always lead to AAM increases in the subtropics. The harsh reality is that where the subtropical SSTAs are increasing the most, in the subtropical western North Pacific, actually leads to poleward anticyclonic wave breaking at the longitude of the exit region of the Pacific jet which corresponds to -AAM in the subtropics and that's exactly what the difference composite above shows.
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This interpretation is just flat-out wrong, zonal winds have not increased in the subtropics, in fact, they've been decreasing in the same period as this SST composite is valid for & they completely oppose the ongoing AAM behavior w/ strong +AAM in the subtropics.
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But these subtropical increases in SSTAs would not contribute to enhanced subtropical AAM because it overlies where the momentum increases are occurring which violates thermal wind relationships. Increase in thermal wind near 45-50N would be a completely different story however because this would be consistent w/ both Hadley Cell expansion and the observed SST distribution but you're arguing that it's contributing to subtropical AAM increases ~30N. It also does not contribute to subtropical AAM due to aforementioned increases in static stability that take place under such a regime to suppress convectively-induced westerly momentum accelerations. Static stability outpaces latent heating contributions because it's not offset by radiational cooling which is discussed in the paper I linked to your response. Global AAM shows no discernible trend since 1976 that would even argue there's a climate-induced signal modulating it which substantially weakens your hypothesis. If anything, we've actually seen more negative AAM in the subtropics during the last 20 years or so, which serves to only further derail your hypothesis.
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"Concordantly, the sub-tropical jet circum-globally has been very strong this month (Nov. 2018) as per the proxy of z200 zonal wind anomalies: The logic attendant this analysis is reasonable and based in sound, fundamental meteorological tenets in my opinion. A more expansive off-equator + SST anomaly will augment additional zonal wind addition thereby modulating AAM response." Subtropical warming in concert w/ tropical warming leads to expansion of the Hadley cells, and while total global AAM could increase in that setting, we should see the mid-latitude jet, if anything, intensify and move poleward in concert w/ these changes even on shorter temporal scales. The strong, equatorward displacement of the subtropical jet directly over the latitudes of heightened off-equatorial +SSTAs undermines this idea & suggests other forcing mechanism(s) are probably at work.
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In order to substantiate your hypothesis you have to separate the influence from both ENSO, the QBO, etc. and then have to show that there not only has been an increase in AAM in the observed record, the increase is significant, the increase in AAM has been occurring long enough for a detectable climate signal to be derived, and that the increase is due to climate and not interannual climate variability, quite frankly that's easier said than done and neither of these papers or your statements or composite from NOAA ESRL showed that. In fact, the second paper notes that increases in equatorial Pacific SSTs favors heightened AAM but they make no further distinction whether this is forced by climate base state changes as you're trying to assert or is simply ENSO being reinforced by subseasonal variability which seems more plausible and easier to substantiate in this case. Before even tackling your idea that simply increases in SST drive increases in convective heating which drive increased AAM, which again completely ignores a lot of other basic processes simultaneously acting to completely dampen this, the idea that there's actually been an increase in meridional SST gradient too is pretty contentious given that tropical Pacific has actually cooled slightly since the mid 1990s, flying in the face of what you're trying to argue plus, the record is simply too short to detect any signal (if there is one) because internal variability is too large. Increases in both subtropical and tropical SSTs actually prove my earlier point about static stability changes because as temperatures increase, the moist adiabatic lapse rate in the tropics decreases and it's been shown by many (including the linked paper below) because there's more latent heating to offset adiabatic cooling which decreases the ascent rate of parcels embedded within this regime and the strength of the Hadley Circulation which is inherently related to its broadening. This also means that while the mid-latitude jets move poleward in response to basic state climate changes, what we're currently seeing w/ tightening and intensification of the Hadley Cell is inconsistent with the long-term trend and what you'd expect in a warming climate w/ expanded hadley cells. Static stability increases faster than changes in heating related to convection because latent heating is offset by radiational cooling. This also means that your notion that warmer SSTs on the whole lead to more convection is also not true if this is a manifestation of long-term climate changes, because static stability outpaces the contribution from latent heating as temperatures warm. https://journals.ametsoc.org/doi/pdf/10.1175/2008JCLI2200.1
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This seems like a reach imo. You simply don't get AAM anomalies like this without their being a substantial ENSO event in place for subseasonal variability to superimpose itself onto, and while I see the line of rationale here it's way too simplistic to argue that the increased AAM is due to warmer tropical SSTs & actually ignores a lot of other basic processes that are ongoing to offset this. For one thing, evidence for that is highly contentious and at best very limited or non-existent, and not to mention the quasi-moist adiabatic adjustment to surface warming actually increases the static stability in the tropics because the moist adiabatic lapse rate decreases in a warmer world as there's more latent heating to offset adiabatic cooling of ascending air parcels, actually making it harder to generate convection in the tropics despite the warmer BL. This is discussed throughout many pieces of literature and is an even stronger counterpoint to the idea that there's a positive relationship between global temperatures and increased convective activity and this is somehow to blame for the higher AAM lately.
