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  1. Singularity

    The Arctic Thread

    @Bring Back 1962-63 (David)'s posts on sea ice thickness, age and the various weather patterns bringing about the multiple patterns we've seen in recent years are in my opinion (and I'm sure many others') an excellent round-up of the situation, the likes of which I've not seen even on the dedicated ASI forum. Some quality contribution from MIA UK (another David ?) as well, on similar areas of the subject. It's a relief (but not surprising) that at least some multi-year ice is still able to be produced; now we just need some to stay within regions that see ice-supportive conditions for more than 2-3 years - something sorely missing in the past decade. Odds are we should gain some 4-year ice to go into next melting season with so that's something. Also - I've been wondering about FRAM export and whether it's really reduced or just appears that way due to the ice melting out further north. Not sure how one goes about assessing that to be honest! It's going to be a really big deal what happens over the coming 5 months in the Pacific and Atlantic-side waters that have higher salinity then ever previously observed. Should the ice struggle to achieve consistent coverage there until record-late (or at all) then the case for a slow-but-sure 'salinification' of the Arctic will gain strong support. This being something to track closely in the freezing season while we wait to see whether any melting seasons are able to 'out-force' the negative feedback of increased ocean-atmosphere moisture transport and bring about a strongly melt-supportive May, June or July (the latter two being the most significant)... and whether the observed fragility of the ice will (in such a scenario) actually mean that we see unprecedented extent and/or area loss rates as a result. Speaking of fragility, I'm reminded of some posts on the ASI forum some months ago that discussed the possibility that the more mobile state of the ice as a result of it being more fragmented and allowing greater wave penetration is resulting in newly-formed ice being less 'pure' with higher saline content than was typical in decades past, making it more vulnerable to mechanical breakdown in particular. Another fascinating aspect to explore perhaps?
  2. Singularity

    2018 Atlantic Hurricane Season

    This seems to be the 'year of the explosively deepening tropical cyclone' and it's got me wondering whether La Nina's legacy of cooler lower-troposphere mean temps plays a significant role by increasing the vertical temp gradients - but I've not (so far, at least) had any luck so far searching for scientific studies on that specifically.
  3. Singularity

    ***Winter Countdown Thread 2018-2019***

    One important thing about all these model projections for ENSO is that they're rooted in what they do with the oceanic component of ENSO, from which they are likely to then assume that the atmosphere will couple and take on a matching ENSO state... but as Tamara has wisely put forward in recent days, this assumption could well be erroneous given how much more the atmosphere has resisted a change to Nino-like in recent months compared to model projections. The associated loss of atmospheric positive feedback then sees the projected versus actual difference grow larger with time. So it may be that the models in general are seeing too much atmospheric co-operation with a Nino-like SST setup, leading to erroneous further warming of those SSTs, leading to erroneous further increases in atmospheric co-operation... and so on. Just my two cents on the matter - I'm interested to see what others make of this interpretation, one way or the other . On a tangent to the above - I've been wondering whether, given the capacity of a descending wQBO, low solar combination to reduce the likelihood of significant stratospheric polar vortex disruption, a weak Nino-like state actually offers lower wintry weather chances than a weak Nina-like state, as the latter works more by the tropospheric pathway to deliver wintry chances in Nov-Dec (but followed by reduced chances Jan-Feb). Or is the forcing under weak Nino conditions (in favour of increased wave breaking via constructive interference with the climatological wave pattern) typically sufficient to overcome the opposing forcing from the QBO-solar combination? So many factors, so few historical cases to guide us! This being a big problem if one attempts to look at historical precedent for combinations of more than a few teleconnections; you soon end up with too few years within each combined category to be able to draw significant conclusions from. Hence we find ourselves having to try and use an understanding of the processes to anticipate in advance what might be the consequence. Arctic sea ice is a particularly big deal here as - IMO - recent years have seen the autumn-early winter deficits cross another threshold beyond which they can begin to influence the atmosphere in ways that go beyond the weakening of the polar jet. A few others have already mentioned the main aspect of this; frequent and at times unusually persistent displacement of the 'focal region' for deep cold at the high latitudes toward mid- or even lower-Canada/Greenland and associated encouragement for the polar vortex to spend time there rather than nearer the N. Pole. There may also be some possibility of a secondary focal region in the vicinity of Siberia, making it difficult for the stratospheric vortex to achieve stability, but this is highly speculative and in any case both pattern alterations require many more years of supportive observations to have much confidence in. With such a weak ENSO state, this autumn-winter-spring ought to be a good test of the theory. It's going to be fascinating to see what happens (one way or the other...).
  4. Singularity

    Teleconnections: A More Technical Discussion

    For winter forecasting these years, one of the biggest wildcards - and one which @Blessed Weather wisely referred to in his excellent QBO-Solar-ENSO research update - is the effect of Arctic amplification, as it seems that this has in recent years been driving more frequent and at times stronger wave breaking that might otherwise have been expected, as a result of the more amplified tropospheric patterns relating to the weaker polar jet stream. In fact, I think it's particularly problematic when the QBO-Solar combination favours a strong polar vortex, as we may face a situation in which the vortex is perturbed unusually frequently yet could strengthen rapidly as soon as it had the chance to do so... with the difference in consequences being between numerous cold air outbreak opportunities and predominantly benign or unsettled weather depending on your location. We saw this back in late 2016, when the vortex was highly perturbed Oct through mid-Dec but then, when the wave-breaking took its first breather, rocketed to record-strong levels by late December. Unfortunately, what went on during and after that time across the U.S. and Europe is not a handy guide for this coming winter, due to the very strong El Nino forcing that was in place back then. Generally, my impression is that Arctic amplification as having the greatest potential impacts on both stratospheric and tropospheric weather patterns Oct-Nov, decreasing slowly during this time, as the Arctic sea ice grows and cold air pooling develops (albeit not as much as it used to). Dec is then the most uncertain month as the balance of power becomes even early in the month then shifts in favour of other teleconnection forcing by mid-Dec. Should Arctic amplification continue to grow more extreme as most modelling/forecasting anticipates in the coming decades, I believe that the balance of power may take until increasingly far into the season to shift, which raises all sorts of interesting (and from a forecast standpoint, concerning) possibilities.
  5. Singularity

    Teleconnections: A More Technical Discussion

    Well then. In the week that I've been away on holiday, the surface warmth has suddenly made some pretty good progress all things considered. I must admit I didn't expect to be seeing so much warming to the east of the area affected by the wide WWB that recently took place between 180 and 100W. Meanwhile, the South Pacific looks to have seen some areas of warming, and the N. Atlantic has the least widespread or strong negative anomalies that I can remember seeing it in a while. The eastern tropical Atlantic seems to have undergone quite the transformation from cool to warm, too. Is this a wobble or a more significant trend, I wonder? Part of this trend in anomalies may be related to changes in the overall rate of cooling during the autumn season; autumns of decades past cooled at least a little faster as lower total atmospheric moisture and GHGs allowed the heat input April-September to escape at least a little more quickly. Or so the theory goes (which I currently see little reason to disagree with - but I am sure to keep my mind open to alternative explanations). The difference to global mean SSTs mapping may tell a different story for the past week; I'll leave that to others who are more familiar with using that approach. Hope you're all having good weekends, today was impressively warm here in S. UK, in fact record-setting for mid-October .
  6. Singularity

    2018 Atlantic Hurricane Season

    Leslie's now wandered so far back southwest that some tropical-level convection can be sustained again (in terms of cloud heights). It's also being wrapped around the core very nicely so hurricane status is likely restored. I wonder if these 'wanderer' cyclones may see an increase in frequency should Arctic amplification bring about a (further? Much debate currently!) decline in the polar jet stream via a reduced Arctic/mid-latitude thermal gradient during the autumn season when activity in the subtropical Atlantic tends to be at its peak. The resultant more amplified ridges seem to apply more of a 'counter-force' against the attraction exerted by mid-latitude troughs as they pass to the N and NE of TCs, meaning it takes a stronger trough to whisk the TC away to the north then/or northeast than before. There may also be an overall expansion of the subtropical highs involved, which is another possible response of the atmospheric circulations to Arctic amplification, but an even more debatable one from what I've seen so far. This year seems to have been a good example of such expansion, but this could be natural variability; other teleconnections coming together in just the right way. I'm still keeping an eye on that Caribbean disturbance with the potential it has down the line. Not looking up to much currently but it could become a 'sleeper' that just about holds on to enough of a surface convergence zone to get up to nasty things once in the W Caribbean or Gulf of Mexico.
  7. Singularity

    2018 Atlantic Hurricane Season

    This could be... trouble. No, not the chart viewer, the storm! ...but seriously though - these model runs look damaging for parts of Greece ?.
  8. Singularity

    Teleconnections: A More Technical Discussion

    Thanks for the extensive bringing together and summary of information David ?. It seems intuitive enough that an overall anomalously warm Indian Ocean would lead to stronger upward motion there, which allies with the Walker Circulation and encourages it to be strong rather than weak, in that way working against El Nino development processes, and vice versa. The same mechanisms may feed back onto the Indian Ocean SSTs/IOD. As usual in climate systems, it's evident that neither has ultimate control here, rather they modulate each other. The Pacific may be the stronger forcing here, mainly because it's larger and has more inertia when you think about the thermocline depth and ocean surface heights.
  9. Singularity

    Teleconnections: A More Technical Discussion

    Looking at the sub-surface anomalies, there's plenty of anomalous warmth building up. It seems to me that we're witnessing in the tropical Pacific a battle between an ocean that wants to release that heat and an atmosphere that's being predisposed against it a bit by a negative South Pacific Oscillation, and perhaps with some further resistance put up by low solar activity. As for the subtropical South Pacific goings on, well, it's intriguing to me that this bears resemblance (allowing for the 180 flip between hemispheres) to the pattern we saw across the N. Atlantic in May-July this year that coincided with an anomalously strong Azores High. Perhaps the pattern in the S Pacific is tied in with the strengthened subtropical high there, and by causal chain, the negative SPO? Generally, the oceans have shown more of a 'store heat' behavioural pattern this year. The tropical Pacific SSTs are still likely to achieve at least intermittent El Nino strength as @Bring Back 1962-63 indicates using historical precedent and due to the anomalous heat at depth discussed above, but the overall global SSTs may be at a different point in the usual cycle that sees the predominant ocean-atmosphere heat exchange oscillate between storing at ocean depths and releasing into the atmosphere. If true, it could be another 1-5 years before the oceans take on a predominantly warmer than usual appearance again. This, however, is subject to the influence of climate change... what went before may not apply so well in the years and decades to come.
  10. Singularity

    2018 Atlantic Hurricane Season

    Great summary as usual @Bring Back 1962-63. Fascinating developments - you can really see the upper-level outflow in the WV sequence, the hallmark of sustained intense convection. The slow storm motion looks the main inhibiting factor; the shallow seas can't offer sufficient fuel for very long at any particular spot.
  11. Singularity

    2018 Atlantic Hurricane Season

    That even comes close to the mother of all sucker punches as the ridge builds north of the renewed Florence. Hopefully just another manifestation of GFS' storm-happy mode of late... it's been making deep lows here, there and everywhere - you'd think it was GEM! ? Following your analysis with interest. I do wonder if Isaac might get up to something again. Not had time to check on it today but your earlier post indicates a very real possibility of regeneration. Could 2018 be the year of the undead Atlantic TCs? ?
  12. I really hope this apparent eyewall building is a red herring and not a genuine response to being so near the coast still and with such sodden ground beneath the core. Regardless, the 'doom belt' continues to rage on the NE flank. Or so I've heard it called, among many other names, some unrepeatable on here.
  13. There's the frictional effect I mentioned earlier. Chewing its way along the coast for a little while longer.
  14. I believe the decelerating and left-refracting effect of the land on the wind can potentially help a TC tighten up its core . Most TCs spend too little time in the right position to utilise that but this one is a major exception. This may be behind the improved visual presentation despite little actual strengthening (though I would argue that a small bump up to 100 mph sustained winds is justifiable based on some obs I've seen). The friction could also be a factor behind the fact that there have been a number of 'crawler' TCs that have seemed to show some resistance to moving inland when that land is to the N, NW or W; the E and NE quadrants of a storm usually have the strongest flow, and as a result, the stronger potential effect on storm motion. A fascinating case study. If only there wasn't so much in the way of real land, environment and livelihoods being devastated ?.
  15. Florence's core struggles remind me of those had by Irma last year as it grazed Cuba. Unless I'm recalling incorrectly, a common factor between the two storms is therefore dry air in close proximity during an eyewall replacement cycle. It seems, then, that during this process, some dry air becomes entrained and becomes so entwined with the new developing eyewall that the cyclone then has a hard time getting rid of it. This dry air interferes with the eyewall in a manner that causes irregularities and sometimes breaks large enough for some escape of warm air from within the eye, further lowering the efficiency of the storm. A downside to these struggles for anyone in the path of the cyclone is that the less efficient storm can't contain its energy so well, resulting in a larger field of strong winds and hence a larger potential storm surge. I literally just came up with that theory as a few ideas bounced together in my head. Please don't hesitate to correct me if anything I've said doesn't make physical sense ??.