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8 hours ago, Blessed Weather said:

Thanks for starting the SSW discussion David. I hope over the coming weeks there’ll be some great analysis and discussion. For those of us interested in the stratosphere it’s been a fascinating winter with lots going. In this post I’m going to try and highlight what I saw as the key developments over the winter that had a bearing on the eventual SSW.  

A Review of events leading to the 2018 Sudden Stratospheric Warming (SSW)


Malcolm, what a brilliant and comprehensive post which obviously took you a great many hours to prepare and research. This is a wonderful way to contribute to the "Great 2018 SSW Debate". Your charts and explanations are really clear and easy to follow.  I'll need to re-read it several times and study all the charts and diagrams very carefully. I particularly like the way you went through the changes in the stratosphere from last November and right through the winter.  :)


I think that many posters in this debate will be considering various aspects of this historic SSW event - the build-up, the timing, the causes and the impacts. I hope to see many comparisons to past events - both full on SSWs and those that failed to materialise. I would, briefly, like to pick up on a couple of things that you mention and perhaps help to generate a wider debate.  I am intending to make several quite lengthy posts myself during the next few days and weeks but this post is just a short follow though on yours. I have only copied the very top bit above but I'll try to make it clear which points that I'm referring to.


Whilst the MJO was undoubtedly an important contributory factor, I wonder if in terms of a "cause and effect" relationship it is rather more the latter than the former. I have read various quite conflicting reports on this, several of which you refer to. Sometimes the GWO phases and AAM processes are rather ignored by some writers/posters (certainly not by your good self).  I went through this process in part of my first post on page one of this thread and the dates and timing of the changes. We saw the temporary slight weakening of the east Pacific based La Nina during mid January, then we saw a spike in relative AAM from a negative position through to a positive one. This spike led to the GWO moving through its phases. with +ve FT and then +ve MT with the usual time lags between the phases. EAMT was still -ve in late January and only started to rise from January 26th/27th going +ve around the turn of the month and during the first week of February. I am gathering evidence where I hope to prove that this +ve EAMT was a strong contributory factor to the final triggering of the SSW - again with the usual 10 to 14 day time lag which fits in perfectly with all the timings and I'll report back on that in a few weeks time in a separate post. The MJO had previously approached it's key phases of 7/8/1 in late December 2017. Although there had been a brief spike in AAM just before Christmas, it then nosed-dived. The -ve AAM and the moderate La Nina really suppressed the MJO that time around so it had very little influence.  Then (with it's usual 30 to 45 day cycle) the MJO was next set to reach it's key 7/8/1 phases in early February. It had already reached decent amplitude during its maritime phases 4 and particularly 5. This may well have been due to the temporary weakening La Nina in the second half of January and the spike in AAM combination.


So far, this is dealing with what "caused" the MJO to gain amplitude. We still need to examine why it obtained almost record amplitude as it reached phase 6 and on into phase 7 and this will be fascinating as the debate gathers momentum. Then we need to study the "effect" part. How much of an influence did the MJO have on the precursors to the SSW. Although I hypothesise that +ve EAMT "might" always be a strong contributory factor that certainly doesn't rule out all the other drivers (including the NAMT) and we'll need to examine these very carefully.  Finally, I feel that we'll learn more about the 2018 SSW by comparing it to a number of previous events. I've been struggling a little to obtain suffient archive input but this is a forum wide effort and I hope that we can piece the jig-saw together to make sense of it all so that we can draw some realistic conclusions.  David :)  



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We are delighted to say that we have just launched our “Teleconnections Research Portal”. There is a direct link below this statement. This is an exciting new facility which is available to all the 33andrain forum members and visitors. It is intended to provide specialist assistance for everyone who wishes to learn more about teleconnection science from the basics through to much more advanced theories and technical information. For example, if you want to understand more about the Madden Julian Oscillation (MJO) or dig deeper into the causes or effects of a Sudden Stratospheric Warming (SSW), this is the place to visit. If you are learning about the El Nino Southern Oscillation (ENSO), Atmospheric Angular Momemtum (AAM), North American Mountain Torque (NAMT) or a whole array of other teleconnections, then this research portal is right for you. Its primary function is to provide a back-up support to this "Teleconnections: A More Technical Discussion" specialist thread. The portal offers the following features:

  • An extensive library facility with links to abstracts and summaries of papers with a direct link to each full paper.
  • An "Introduction and Welcome Page" explaining what the portal offers with direct links to other parts of the facility.
  • A "User Guide", explaining how to use the portal, how to "Search By Tags" and a "Key To Tags".
  • A comprehensive "Index To Papers and Arcticles" with a full listing of all the titles under many topic headings.
  • A "Glossary of Terms and Short Definitions" which is still slowly evolving and will be added to during the coming months.
  • An "Interactive Area for Members - Feedback and Comments" where we wish to encourage participation from any of you.

We already have a great range of papers and topics in the portal and our initial focus was on Sudden Stratospheric Warming (SSW) to back up the debate into the 2018 SSW event which was launched on this thread a few days ago. We already have over 100 titles and links to papers in there and these will constantly be added to. You may well have comments to make on specific papers and the "reply to topic" option is available under each paper review.  You may have links to papers that you would like us to add to the portal. We explain what is required in our "Interactive Area" and we would love to hear from you - we can "all" benefit from this and help each other.


We have plans to develop the portal further. This includes a specialist "Learning Area" which may be ready early next year. We will always appreciate your feedback and if you have any ideas for improving or developing the portal, please post them in the Interactive Area, so that we can all consider them and comment on them. Above all, this is intended to be a friendly environment where we will always welcome all members. Let's make it work for all of us.  So please have a good look around the portal.  I hope that you like it.   David




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MJO Developments - Part 2


Following on from David's comprehensive post (above) my 'Part 2' analysis is a brief look at the very latest developments and forecasts.

The signal for MJO activity to initiate in Africa (Phase 8/1) that models were picking up on is now taking place, as suggested by the increased rates of rainfall expected 4th - 9th May. Source:


Rainfall forecast Africa 4May2018 Ventrice 30w 5S-5N marked.jpg


 All major international models are now firming up on forecasts that MJO activity will progress through to the Indian Ocean (Phase 2) by mid May. Here are the latest charts from ECMWF (to 18th May) and GEFS (to 16th May). Source:


MJO ECM 04-18May2018.gifMJO GEFS 02-16May2018.gif


The MJO is notoriously difficult to forecast, with regard accuracy falling away after 5 days, so the following analysis should be viewed in that light. But it's interesting that the European Centre for Medium Range Weather Forecasts ENOM model's forecast for the period 4th May to 4th June suggests the MJO will progress through Phase 2 and possibly into Phase 3 at low amplitude.


MJO Phase 4May to 4June EMON.gif


A look at the MJO Phase 3 composite 500mb geopotential height anomaly for May shows a negative anomaly centered over the mid states. It may be just a coincidence (as other factors are at play and it's a weak signal), but it's interesting to match this with the latest NOAA precipitation forecast for May. Whichever, it's not an encouraging outlook for settled weather over the coming month.


MJO Composite MayPhase3all500mb.gifCPC_30_DAY_PRECIP_May2018.jpgS



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Before I migrated across to the 33andrain forum, I used to post frequently on a UK forum. One of my regular features was to look at Arctic Sea ice extent and air and sea surface temperature profiles as well as snow cover extent In the Northern Hemisphere. I would then focus on the impacts on UK and Eurasian conditions.  As this is essentially a US weather forum (with some global members), I will slant my contents and comments more towards North America. 


Due to time constraints, I am splitting this post into three parts. In part 1, I will look at the current Arctic conditions as well as an overview of winter 2018. In part 2 (towards the end of this week) I will look at the conditions at the time of the 2018 Sudden Stratospheric Warming event and the impacts following this, with a North American focus and snow cover maps. In part 3, I will put the current Arctic conditions into a longer term context and I will consider where this fits into the global warming and climate change debate - taking a neutral and non-political stance. I will review several papers on this part of the subject. Some of these are already in our (click on the title for a direct link) Teleconnnections Research Portal which is really taking shape with a wide diversity of topics.


Arctic Sea Ice News and Analysis:

I was keeping an eye on the latest information produced by the excellent (click on the title for a direct link) National Snow and Ice Data Center (NSIDC). This is updated daily and shows the current ice extent and related data.  They also produce a monthly report and the most recent of these was published on 3rd May, 2018 and is available on the same link as above. This includes a review of the changes during April. Let's have a closer look at some of the recent charts and I'll comment on these below each chart:


The chart (above) shows the current overall sea ice extent over the whole Arctic region. The orange line is the median and shows the edge of the ice cover averaged over the 30 year period from 1981 to 2010. The ice extent reached it's winter maximum on 17th March, 2018 (see chart below) and has started to decline since then with the Spring/Summer melt now well underway. The mauve line in the chart below represents the median for the maximum annual ice extent. 


I also include an Arctic map (below) to identify the locations of all the seas that make up the Arctic Ocean so that I can comment more meaningfully on the local variations. You can see that ice extent was and continues to be below average over much of the region except in Baffin Bay. In March it was also above above in the Sea of Okhotsk but most of this thin ice has already melted during April. Sea ice build up and extent had been well below average in the Bering Sea throughout the Winter and what ice was there has completely melted during the last few weeks.  In contrast, the ice extent has been very different on the Atlantic side of the Arctic. In fact the maximum annual extent was reached towards the end of March and in early April and has declined only very slightly since then with melting mostly confined to around the St Lawrence seaway, Newfoundland, parts of south-east Greenland and the Baltic Sea (east of Denmark and further north).  The Hudson Bay normally remains frozen for at least a month later than the the other peripheral areas and looks set for a very late melt this year.



The sea ice concentration map gives us a good clue of where imminent melting is mostly likely.  The darker shades of blue are likely to be almost completely ice free within a few weeks.  The rate of melting is related to prevailing wind patterns (with stronger winds from warmer sources leading to a faster melt) and cloud amounts (the albedo effect of white ice reflecting sunshine, is stronger under clear skies and reduces the melt rate). These and other local influences can lead to wide variations from year to year.


To put 2018 into context, the chart above shows the exceptionally low ice extent over the late Winter to early Summer period.  The 2018 values are shown in blue and the dark grey line shows the 30 year median. The hatched line shows the record low year of 2012 which was attained in September of that year (not shown) but it was amongst the lowest from mid May 2012 through to early Winter 2013 prior to a modest relative recovery. Very worryingly, 2018 has seen overall ice extent (for sea areas with at least 15% ice cover) running well below 2012 levels. The pace of melting in an average year, greatly accelerates during May and particularly in June. This rate was quite exceptional in 2012 but right now it looks like the 2018 melting trend is showing little sign of slowing.


The chart above focuses on the recent years, with the previous 4 years (from 2014 to 2017) plus 2012 shown. 2018 has seen closest to lowest levels on record. 2017 was slightly lower for short periods in January and March and in the last few weeks 2018 and 2016 have been running neck and neck as the lowest. Although 2016 saw rapid melting during May, it was overtaken by 2012 during June. I will keep tracking the relative 2018 values.  I will provide very brief monthly updates on this thread and another longer review around September when we can look ahead to next Winter.  


Whilst fresh "thin" ice build up during the Winter will generally disappear much more quickly earlier in the melt season, the extent of older ice is much more important.  The charts above reveal some even greater concerns. The top two charts compare the age of ice at week 9 (the beginning of March) in 1984 and in 2018. The old ice is generally much more compact and far less prone to melting and will very likely survive the summer melt. In 1984 the extent of ice more than 5 years old (shown in red) was far greater. In 2018 almost all the 5 year old+ ice has disappeared and there is hardly any 4 year old (yellow) remaining either. There is some 3 year old ice (green) but most of the ice is 1 to 2 years old (the blue shades). The bottom left chart above shows proportions of each of these ice "age" bands. There was little change from 1984 to 1989, then the oldest ice declined steadily from then until 1993 before stabilising again until 2006. The next 7 years saw a rapid decline of older ice down to much lower levels. Although the amount of 5 year+ ice "appears" to have stabilised since 2013, this is very misleading as there is so little of it anyway. The amounts of 4 year+, 3 year+ and 2+ have continued to decrease.


There's so much more on this and related matters on the NSIDC site with further links. I will return to some of this in parts 2 and 3 of my report but now onto sea temperatures.


Arctic Current Sea Surface Temperatures (SSTs):

I have spent many long Winter evenings going through the vast amounts of data on the NOAA site, the sub-sites and their archive records. For this section of my report, I have accessed part of their "Environmental Modelling Center and Analysis Branch" on this link:  This takes you to their SSTs page. These are divided into current value and anomaly charts. The top chart on their site shows current global SSTs. You just click on any part of that chart to find the regional charts. The second chart shows current global SST anomalies with the same regional chart access. Let's have a look at the current Arctic charts:                                                                                                             

                                                                                                             SSTs  May 7th, 2018   


The critical level for SSTs is at or below the -1.5c threshold (the purple colour). In calm conditions, sea water will  usually start to freeze when it is below -2c but that is for normal salinity. There is slightly lower salt content in the Arctic (mainly due to snow and ice melt) and the threshold is nearer to -1.5c. There are some areas with SSTs well above freezing between Svalbarrd (about 500 miles east-north-east of the north-eastern coast of Greenland) and off the  north-west Scandinavian coast as well as around Iceland. To put this into context we need to examine the anomalies chart:               

                                                                                                                     SST Anomalies May 7th, 2018 


The anomaly chart shows that there is a wide area of open water in the Arctic with well above average surface temperatures (the white sea areas are still ice covered and not open water (as shown in the earlier ice extent charts). That area around and south of Svalbard has current anomalies widely over 4c above average (the dark brown colours) and over 8c above in several places (the olive green colours). Even with a warming Arctic and and extensively above average SSTs over many parts of the globe, these are truly exceptional anomalies. These appear to be a long term legacy of the 2015-16 winter when the Atlantic jet stream powered well into the Arctic for much of the first half of that Winter during the peak of the "super El Nino" episode.  This shifted much warmer than average currents right up to the edge of the main ice sheet. This strong anomaly has persisted for 3 years and shows little sign of reversing. Unless the SSTs reduce substantially, the anomalies might be carried through this summer and into a fourth winter. There is a small area of the North Atlantic, mostly south-east of Greenland and adjacent to the sea ice there with a negative anomaly (the darker blue shades).


I shall pick up on these anomalies and have a wider look at Arctic air temperatures in part 2 of this paper.  That's all for now....TO BE CONTINUED in part 2.



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In the second of my three part Arctic report I will move on to look at northern hemisphere snow cover changes during the 2017/18 Winter and I will examine the conditions following the 2018 Sudden Stratospheric Warming event. This part will have more of a North America focus while part 3 will look into the impacts of the declining Arctic sea ice and at some of the global issues.


Northern Hemisphere Snow Cover Analysis During Winter 2017/18:

Excellent snow cover charts are produced by NOAA.  When you go to their site you can change the date range and go back over 10 years. You can animate the charts to go though any selected set of dates and then change the speed and pause on any particular day. You can also switch to a North American view or an Asia and Europe view. These are brilliant, very informative charts and great to play around with. I’ve re-set the link below to show the entire period from October 1st 2017 to May 1st 2018 but you can change the dates on the site and choose your own options. Just click on this link:  

I show below the snow cover and sea ice changes for 1st of each month from October 1st 2017 through (thru) to May 1st 2018 (comments afterwards):

                                           October 1st 2017 chart                                                                                          November 1st 2017 chart   

 ims2017274.gif  ims2017305.gif   


                                           December 1st 2017 chart                                                                                          January 1st 2018 chart 

 ims2017335.gif ims2018001.gif


                                           February 1st 2018 chart                                                                                          March 1st 2018 chart 

ims2018032.gif  ims2018060.gif


                                              April 1st 2018 chart                                                                                                May 1st 2018 chart

ims2018091.gif  ims2018121.gif

As in several recent Winters, snow cover developed earlier and more extensively in northern Asia and Siberia than it did in North America. It grew steadily from quite early in October and extended southwards across central Asia during November and December and remained extensive right through to April with a covering remaining in northern Asia, Russia and Siberia right through (thru) to early May. 


The snow cover over much of Canada became more extensive during November and into December. There were periods of unusually mild conditions over large parts of the US during this time but with several cold spells around 5th to 10th November in north USA and a very cold outbreak later in December and into early January, particularly around the Christmas to New Year period with snow cover extending across all of the northern states and further south at times. This retreated in the second half of January prior to another cold snap in early February (mostly affecting the north-eastern states).  Very mild conditions followed across much of the US up to mid February. Then there were some exceptional contrasts between some exceptionally cold conditions in Canada and mostly milder conditions in the US.  This cold seeped southwards at times to affect the northern states.  This contrast continued well into March, when a very cold outbreak extended down the eastern states as far as northern Florida. The second half of March and early April saw repeated surges of cold (sometimes very cold) air mostly into the north-eastern states. Some unseasonably cold conditions in mid April were seen extending into the western states and a swathe from central to parts of the eastern states.  This even reached the central southern states. This was followed by a rapid warm up within a couple of days and then another surge southwards of cold air into the the central states with some exceptional temperature contrasts. These abrupt changes continued through (thru) the second half of April.  Although a typical Spring will see a battle between the remnants of Arctic air to the north and much warmer Gulf air from the south, I believe that some of these contrasts with so many rapid changes is very unusual (some reasons offered in the next section) although my experience is much better suited to analysing UK and European weather patterns and I'll happily stand corrected (please feel free to comment).  Not surprisingly, snow cover during this period was variable with retreats and expansions throughout late March and much of April. By early May the general lowland snow cover had retreated to Alaska, northern and particularly north-east Canada. 


A Look at the Arctic Impacts During the 2018 Southern Stratospheric Warming (SSW):

 I refer you to the superb post from @Blessed Weather (Malcolm) towards the top of this page, entitled "A Review of events leading to the 2018 Sudden Stratospheric Warming (SSW)”.  His excellent analysis looked at the weather patterns, the QBO,  the MJO, the ENSO state, changes in AAM and the torques, the jet stream and particularly the stratosphere from November right up to the time of the SSW. This occurred on 12th February, 2018 with a full wind reversal in the stratosphere that lasted for 17 days but we had around a 2 week time lag until it propagated down to the surface to reverse the flow over the north pole and then over a much wider area. There were several further renewed warmings and further impacts before the final warming around mid April. I copy one of Malcolm's charts (below) showing the stratosphere changes, the major SSW and the further warmings that followed:




Let's have look at the surface flow patterns and reversals over the Arctic following the impact.  I comment below each GFS archive chart (all are T+6 - so effectively "current" at the time):


Initially, the Tropospheric Polar Vortex (TPV) remained intact over north-east Canada and Greenland with low pressure (LP) over much of northern Canada and the north-west Atlantic.. An Arctic high pressure (HP) has already formed just to the east of the north pole with a ridge extending through Scandinavia, northern Europe and towards the UK.  A belt of HP extends across much of the US and north-east Pacific and starting to link across the far side Arctic from the Aleutian Islands through (thru) to Siberia and then westwards across northern Asia and southern Russia. Meanwhile LP has replaced the normal quasi-stationary Azores HP as well as across southern Europe with an easterly flow developing there.



Just 4 days later,  we see the flow reversal really starting to become established. The TPV is weakening and starting to be displaced north-westwards with HP developing over Greenland and linking up with a vast belt of HP, centred north-west of Scandinavia and extending right through the eastern side of the Arctic, Siberia and to the Kamchatka Peninsula as well as linking through Russia and northern Europe.  The LP near the Azores has deepened in situ as has the LP now extending across all of southern Europe enhancing the easterly air stream which now extends from Siberia, through Russia, northern and central Europe, the UK and well out into the Atlantic.



After another 4 days, we see further dramatic changes. The TPV has rapidly transferred across the Arctic and completed its journey from Canada to Siberia. Meanwhile it has been replaced by an exceptional build of pressure across northern Canada and extending across much of the US right down to the southern states. The Arctic HP has moved back over the north pole linking to a powerful HP over Greenland. The LP near the Azores has been absorbed into the deepening LP over southern Europe. Two new areas of LP have developed off the eastern  and western US sea boards.  Note the inverted pattern with the sub-tropical HPs being replaced by LPs with the HPs over the Arctic and North Atlantic.  This was reflected in both the Arctic (AO) and the North Atlantic (NAO) oscillations being strongly negative at this time (as can be seen in the two charts below). The surface flow reversal is now quite exceptional. In the middle latitudes the prevailing westerly or south-westerly flows are now easterly. The easterlies can be traced from northern Asia, Russia, Scandinavia, much of Europe, the UK, the whole of the Atlantic, into Newfoundland and the north-eastern US, dipping slightly south and then north again across the central US states, continuing right through the north-western US states and out into the north-east Pacific through (thru) to the Aleutian Islands, then dipping south slightly and on to the Kamchatka Peninsula and north-east Asia and back to Russia. In other words at this time (2nd March, 2018) we can trace a full surface flow reversal across the entire northern hemisphere. This is extremely unusual, perhaps almost unprecedented even during previous major SSW events with full surface impacts. I'll have to do another post in a week or two, comparing this chart to the peak of the  impacts from earlier SSW events as part of our "SSW Debate" to confirm my assertion.

ao 11.5.18.PNG 


nao 11.5.18.PNG



With a full on SSW, we not only see a flow reversal with high and mid latitude blocking patterns we also see the jet stream pushed into taking a more southerly track. This was strongly evident for a prolonged period following the initial impacts of the 2018 event.  The 2nd March shows the northern branch of the jet stream, very weak, broken and bucking.  There is a small segment looping from Newfoundland, over Greenland and Iceland and then returning south-westwards.  This was around the periphery of the intense Greenland HP.  Another segment is pushing south-westwards from north-west Canada out into the Pacific before turning eastwards to cross the mid US from west to east and joining a southerly streak pushing eastwards across the southern US states. This branch strengthens as it exits the US eastern sea board and then pushes even further south to hit southern Europe, the Mediterranean  and well into north Africa.  At one stage it even reached the northern Sahara Desert. The northern side of this main branch then weakens, while the southern side pushes yet further south to exit Africa over southern Egypt and crossing the Middle East. A weak northern segment links ups with this southern branch over south-east Asia and exits into the western Pacific as a very wide streak. It then weakens again and buckles as it crosses the Pacific. I'll return to this below.



By 6th March, we can see the first signs of a slight relaxation of the SSW's grip.  I remember the initial impacts on Europe being described as the "Siberian Express" with the touchdown in that region which then spread rapidly westwards, through Europe, across the Atlantic and then the US. It was as if it had all happened so quickly that it ran out of steam - I joked in a UK forum post that it had "overshot the platform"! There is still a flow reversal  showing with HP over Arctic, extending eastwards into Siberia and south-westwards into Greenland, Canada and the western US states. The HP is now rather weaker.  There is quite a deep LP over Russia (unusually deep for that region) but with weak and slack LPs over the central US states and in the western Atlantic. The LP over southern Europe has drifted northwards. Now if we take a quick look at the jet stream again (below) we can see that it remains on a far southerly track. I remember this period of a week to 10 days or so, through (thru) to mid March where we saw a number of "rudderless" LPs meandering slowly around.  With no jet stream to steer them they were simply filling the void between the weakening HP belt to the north and jet stream so far to the south. This was a very benign period for the mid latitudes across the US and Europe.




I now jump to 17th March.  Surely, this unusual slack period could not continue for too long and something would have to give - either the jet stream would find its way back into its more usual position or we would see a renewed surge of cold air? Referring back to the stratosphere chart, those two further warmings that followed the initial event on 12th February occurred towards the end of February and the turn of the month into March. Again we saw about a 2 week delay before there were surface impacts. This time, with the legacy of the initial SSW still imprinted on the atmosphere, there was a far quicker response. The chart above, shows renewed HP across the Arctic stretching from central Asia and Siberia through (thru) to northern Canada with another link extending southwards into Greenland and again across to Scandinavia.  All these HPs were rather less intense compared to the initial impact. The distribution of LP was different to before with a fairly deep one centred over Svalbard and extending into northern Russia and a large but weak LP in the north-west Atlantic. Southern Europe again saw a wide band of fairly shallow LP.  The easterlies returned very suddenly across northern Europe and the UK. Meanwhile, the US and much of Canada continued to experience very benign conditions and very slack pressure patterns. 



This secondary impact in Europe eased very quickly within a few days but just as before, the impacts of these secondary or multiple warmings pushed westwards. HP built strongly over north-eastern Canada and combined with the Arctic HP. The flow reverse was evident in the western hemisphere with long fetch northerlies pushing into the eastern US states and then westwards into the central states.  By this time the Azores HP had finally reasserted itself. 


The jet stream was taking a different route. In the US, the main branch was further south compared to the time of the initial SSW impact but after exiting across the southern states and Florida it then looped northwards and then eastwards across the north Atlantic before diving south-east towards Spain and the Mediterranean. A southerly branch pushed through North Africa and the Middle East before weakening and buckling again.



I must stress that although the initial SSW and the further warmings that followed all impacted very strongly on the lower tropospheric and surface pressure patterns and the path, strength and trajectory of the jet stream and were the main driving forces from mid/late February until well into April, there were other influences too. The weakening (but continuing) La Nina, the MJO and relative AAM and the torques all played a part too and we see changes in the seasonal wavelengths as we progress through Spring with the normal northward migration of the jet stream (well delayed this year), the warming land surfaces under an increasingly stronger sun and the normal thawing of sea ice and snow cover well underway after the March equinox (again delayed this year and described in the first section of this post and also in part 1).  So, while we continued to see residual influences of the SSW, it's much more difficult to pinpoint the exact causes of the weather impacts for late April into May. Typical Spring weather in the US and Europe sees a mix of early warm spells but with at least a few reminders of Winter with some cold snaps too.  I highlighted in part 1 that what has been unusual this year, even for the US, is the sheer number of short term variations and some quite exceptional temperature contrasts over short distances and almost from day to day.  I shall now return to the main impacts and look at the surface temperatures in the northern hemisphere during the key period.



So, back to 2nd March.  Very cold air had pushed right across from Siberia, Europe and the UK producing sub zero temperatures. This was the UK's coldest and snowiest weather for at least 7 years in most parts (since December 2010) although some locations saw more severe conditions in March 2013 following the previous strong SSW.  Many UK weather stations recorded their coldest March day on record.  At this stage over most of the the US it was unseasonably warm with some very cold air just starting to show its hand in northern Canada. The 850s (below) were even more impressive. The lowest upper temperatures were actually in place from later on 28th February until early on 1st March.  I know that you frequently see sub -10c and sometimes sub -20c values in parts of the US but the UK rarely sees values below -10c and the whole country was under sub -14c temps and some parts managed below -18c for a short period. This is truly exceptional even in January but to see these values in early March was quite extraordinary, thanks to the SSW.



Now let's find some of the US extreme cold.


The initial impacts of the main SSW, did not produce widespread cold across the US.  Parts of the north-east as well as much of Canada saw some very cold conditions. The 6th March chart (above) shows some deep cold just across the border in Canada and some of this filtering into the western as well as the north-east states.  Several cold incursions reached as far south as northern Florida (see below).



Then if we move forward to the second impact, this reached North America in the final week of March. The values in the chart above are for 1400 on 25th march. with large swathes of the eastern and the western states sub zero with sub -8c max temps in quite a few locations. I know that some parts of the US saw much lower values earlier in the Winter and this illustrates how an SSW has different impacts around the northern hemisphere. Let's look at the 850s. 


Some of the lowest values occurred on 19th March with sub -20c and even sub -24c temps reaching down across the north-eastern states. While Europe had already seen it's coldest weather impacts from the SSW in early March and again just after mid March with further cold snaps into April, the US saw some of its coldest impacts during April.  For much of the first half of April, there was a huge pool of sub -24c 850s (and some sub -32c temps) lurking just across the border in southern Canada.  This pool extended southwards at times well into the heart of the US and particularly the north-eastern states for quite longer periods.  The 4th April chart below being a typical representation. I imagine that these were pretty exceptional even by US standards for April (and judging by some of the comments on several other 33andrain threads) 



Surface temps were pretty impressive too during this period. Of course while a major SSW displaces much of the Arctic cold air towards the middle latitudes, it leaves the Arctic itself in far less cold conditions. Even in recent years without a major SSW we have seen some very cold incursions into North America with a shift in the TPV and sometimes temperatures over the high Arctic getting above freezing even in mid Winter. Some theories suggest that this is part of a pattern associated with climate changes and global warming. I shall focus on this in part 3 of this Arctic report (due in a week or two). 


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What is the GSDM and how does it help with subseasonal weather forecasts? - A Review of This Presentation


This specialist "Teleconnections" thread was set up to examine and learn more about the main drivers and influences on the broader global weather patterns and how these drivers interact with each other and which are the more dominant ones. Some of the posts have already focused on the great importance of understanding the major role played by AAM (Atmospheric Angular Momentum) and the torques. Several of us have discussed the GSDM (Global Synoptic Dynamic Model) which was jointly developed by leading meteorological scientists Edward K Berry and Dr Klaus Weickmann while they were working at NOAA in the late 1990s and earlier years of this century. They also devised the GWO (Global Wind Oscillation) as a way of plotting and measuring the amounts of relative global AAM,  FT (frictional torque) and MT (mountain torque) at different phases of the cycle. They became leaders in this specialist research which has been used to assist in understanding impacts on global weather patterns and upcoming changes up to a few weeks ahead. 


Unfortunately, they left NOAA several years ago and it seemed that their vitally important work had ceased with a great loss to advances in meteorological science.  We have been trying to track them down and recently found an email address for Ed Berry. I sent Ed an email and I was delighted when he replied almost immediately. He explained that Klaus Weickmann retired several years ago. Ed Berry (Senior Weather-Climate Scientist) continues his excellent work on the GSDM and retains his lifelong passion to develop the model and its meteorological applications further. We have exchanged a few more emails with Ed and he is very supportive of the work that we are doing on this thread (as well as with the Teleconnections Research Portal). I hope that we can persuade Ed to post on here in due course.


I asked Ed if he could assist us with obtaining past AAM, FT and MT data (which had been withdrawn from the NOAA Maproom archives) as well as more comprehensive current data and I explained to him that we had been in touch with Victor Gensini (Assistant Professor, Department of Geographic and Atmospheric Sciences, Northern Illinois University) who has been working  on and producing some of this missing data - several of our posts include examples of Victor's charts. Ed told me that he was in touch with Victor and they had discussed some of this work.  Victor hosted an AMS seminar recently (American Meteorology Society - Student Chapter,  College of DuPage, Chicago on 28th March, 2018) and Ed gave a one hour presentation on the GSDM (as shown in the title to this post). Ed emailed a  link to his presentation last week and I have already viewed it three times, learning a little more about the GSDM each time. He gave me full permission to review it on here. Firstly, here's the link to the Research Portal entry:


What is the GSDM and how does it help with subseasonal weather forecasts?  (A YouTube Presentation)


Just click on the title which will take you to a summary and from there you'll find a direct link to the 1 hour and 4 minute presentation.


It is a brilliant seminar with clear charts and explanations, ending with a question and answer session. For anyone wishing to learn more about AAM, the torques, the GWO and how they interact with other major teleconnections like phases of the ENSO (El Nino Southern Oscillation) and the MJO (Madden Julian Oscillation) then this is absolutely essential viewing. I also strongly recommend  this for more advanced viewers as well. The presentation is right up-to-date and includes the 2018 SSW (Sudden Stratospheric Warming) event and links to key issues like climate change. Much of the presentation is slanted towards the North American climate and US weather patterns but it has a global significance and includes impacts on both hemispheres. I show a small selection of the charts from Ed's presentation below just to whet your appetites:




































Obviously one needs to follow the full presentation to see what is behind these charts. There is also a focus on several earlier events including Winter 2012/13. I hope to have many more exchanges with Ed as well as with Victor. I feel that if we ask them a few questions that we may well encourage them to contribute by answering directly on this thread. David



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This is a post to describe an often forgotten feature of the global climate, the Southern Hemisphere. I am going to discuss how the climate drivers affect climate in the Southern Hemisphere, and provide a resource for people in the Southern Hemisphere on how weather patterns there work. Firstly an extract from my blogpost last year about the Southern Annular Mode.


Southern Annular Mode


"So the Southern Annular Mode or SAM (or Antarctic Oscillation or AAO) is basically an index showing how far equatorward or poleward the sub tropical ridge is, and therefore the polar jetstream. 

The polar jetstream is below this ridge of highs. In summer, Negative SAM (equatorward for the STRHs), the Sub Tropical Ridge sits over Southern Australia, limiting rainfall and increasing temperatures. When Positive SAM (poleward for the STRHs) occurs in summer, the Sub Tropical Ridge moves south of the mainland and sometimes Tasmania, allowing rainfall often associated with the tropics to fall and temperatures to cool.

In winter, it's a different story. The Sub Tropical ridge and jetstream has moved equatorward with the change of seasons. So in a Negative SAM situation in winter, the Sub Tropical ridge is over Central Australia and allows cold fronts to come through over Southern Australia and give rainfall and colder temperatures. In a positive SAM situation in winter, the Sub Tropical ridge is over Southern Australia and limits cold fronts coming into Southern Australia."


Global Wind Oscillation 

Today I finally finished off my latest article (which seems to be coming an annual tradition around this time of year) on the GWO. This thread has discussed it in detail, but it and the various research articles about the subject out there do not talk about the effect on the GLAAM/GWO in Australia very often. So given it is a global climate driver, I decided to seek out the evidence that would show correlation to my home country's snowfields. Enjoy.


"This article concerns the effects of the Global Wind Oscillation (GWO) and the Global Integrated Atmospheric Angular Momentum (GLAAM or AAM). What these terms refer to is the winds of the planet going in general west (taking into account, polar and subtropical westerlies and tropical easterlies), versus the rotation of the planet. So a low AAM means the planet goes relatively faster than the winds of the planet. And a high AAM means the winds of the planet are going faster than the world spins. So a low AAM means the winds are going faster than normal, and in a high AAM, they are going slower than normal.

So how does this connect to our continent? The GWO and AAM is influenced by ENSO and the MJO, and then back to them in a feedback loop. In general, a negative or low AAM means that there is a La Niña around, and a positive or high AAM means that there is an El Niño around. But there are often breaks with this correlation, like all correlations do. The MJO is responsible for about 33% of the GWO's effects, the rest is torques and other equatorial waves. The correlations between the GWO and MJO are summed up well in the below chart. 


Generally when the MJO is in Phase 5/6, which are accepted as the best Phases for Australian snowfall, the AAM is neutral or rising into positive AAM territory, depending on various factors, including the mentioned ENSO factors. When the GWO is rising, the convection in the tropics is around Maritime Continent (Indonesia region), just north of Australia. And when it is falling, the convection is typically over Africa, moving into the Indian Ocean. In general GWO Phases 2&3 are for Low AAM, and GWO Phases 6&7 are for High AAM.


Torques account for the majority of the GWO/AAM. These are divided into Mountain Torque and Frictional Torque, and a bunch of smaller ones. Mountain Torque is created when the winds hit the mountains. +MT helps increase the winds, and -MT slows them down. Frictional Torque is similar but the torque is created as the wind scrapes the Earth's surface, rather than by hitting a mountain range. There is a lot of complicated science around the torques and how they get affected by the MJO, and numerous other factors, but the above is a basic summary.


So how exactly does the GWO/AAM affect Australia? Well it turns out it has quite an effect. I compared the GLAAM dataset(spreadsheet fun!)from the NOAA ERSL Physical Sciences Division, and the Spencer's Creek snowdepth measuring site, the generally accepted marker for snowfall in Australia, and the state of New South Wales in particular. Below is the raw correlation between the two. 


So there is a 5% correlation between Australian snowfall and the GLAAM. A -AAM causes more snowfall to occur in the Australian Alps. Other drivers like SAM, MJO and ENSO have higher correlations, but given they are affected by the AAM/GWO themselves, the GWO is still an important tool. There is also the hampers of data analysis to contend with, outliers, errors, etc. 

In other correlations, the GWO also relates to Australian weather and climate as a whole, as well as global climate in general. I analysed this in a 500mb plot from the NOAA, based upon the years that were above +1 in GLAAM and below -1 in GLAAM. 



500mb anomaly plot, +1 and above GLAAM years. 



500mb anomaly plot, -1 and below GLAAM years.

So it is clear there is a correlation between -AAM and troughing in SE Australia, where the major ski resorts are located. And there is also a correlation between +AAM and ridging in SE Australia."


2002 SSW

One thing I wish to discuss is the lack of SSWs in the Southern Hemisphere. Except one. In 2002. It was the year for the only ever major Sudden Stratosphere Warming. There have been many research articles discussing it, including one recently posted to this forum by @Bring Back 1962-63, Peters and Vargin (2015), that discusses it's origin from tropical convection and rossby wave trains. The story goes that convection in South-East Africa and Indonesia started in Early September that year. They turn into rossby wave trains and move south and south east respectively. The Southern Africa RWT moved south towards Antarctica, and the Indonesian one moved all the way to the Southern Atlantic. They then both helped sustain highs in Antractica, one in Eastern Antarctica and the other to Western Antarctica. These two highs caused a strong increase of the planetary wave 2, into the lower Stratosphere, to split the vortex. Several studies show that the vortex split that year was caused by pressure from the troposphere. 


So that's why it occurred? That's how 20 years of a colder and stronger Vortex collapses in one season. But what were the impacts? It completely split the ozone hole, for starters. It was so massive, there hadn't been anything seen like this, in either Hemisphere. The Northern Hemisphere has a major SSW, 0-3 times a season, and we in the South, have one major one in all observable record, but we can say it was the biggest.  


The first article discussed the Southern Annular Mode. The reason why I quoted the article was to explain it, before I say that it absolutely tanked in the Stratosphere. It is a projection upon a situation considered the average in the SH. The SAM in the troposphere and Stratosphere during that month is shown below.


That's a lot of red (-SAM) during Sept, Oct and Nov that year. 

IMG_4338.GIFAnother visualisation of the CPC GDAS dataset, shows how extreme (+36 degrees anomalies) in October from 5-200mb, which is the general region of the Stratosphere. This shows how this was the biggest SSW event in not only the Southern Hemisphere, but the Northern Hemisphere as well.


A comparision which is drawed here in the Southern Hemisphere, is between the 2002 major SSW and the 2012 minor SSW event. But the latter was much weaker than the 2002 event, and not as ground breaking. This is illustrated by the zonal mean zonal wind anomaly chart below.


The difference was a much weaker event, shown by the anomalies. Another key difference was the 2002 already had a weak SPV throughout that winter, which could have lead to the weaker situation, that allowed the 2002 SSW to go ahead on both the tropospheric and stratospheric scale. You can see that with the weaker zonal wind anomalies on the chart above, not only during the SSW, but also before the event occurred.


As for the reason why SSWs don't occur very often in the Southern Hemisphere, that would be largely unknown. The major geological difference is that the SH Vortex isn't surrounded by continents, in comparison to the NH Vortex. This would probably allow the conclusion to be made, that the winds would be stronger around the SH Vortex, because of less mountains and continent. This is also the reason why Mountain Torque is less common in the Southern Hemisphere, because there is less land in the SH, and only one proper main mountain range (the Andes). So aside from that, there is also less wave driving in the SH, because of less continent, torques, etc. Which brings me to the reason I made this. The 2002 Major SSW was largely brought on by two rossby wave trains from Indonesia and South Africa. The conclusion most scientists have made, is that it was largely random in long term climatic timing. Perhaps there may be reasons to do with the MJO/GWO? Or the Northern Hemisphere polar circulation? Lots of questions yet to be answered. I really found this interesting, and I hope you did too. I hope these articles/write-ups help you Northern Hemisphere folk understand how the weather circulation is different in the Southern Hemisphere, because of many factors mentioned here. 


If you want to explore more subjects like this, I'd suggest you take a look at some of the articles in the Teleconnections Research Portal,

like Peters and Vargin 2015. The link is below.



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All About Hurricanes and Tornadoes - A Review of a Range of Papers


With the 2018 hurricane and tornado seasons underway, I feel that it would be appropriate to review a few papers ranging from the basics to rather more advanced topics.  This specialist teleconnections thread is not intended to compete with any other threads but is designed to complement them. While the seasonal threads such as those on hurricanes, storms and tornadoes etc come and go, this thread retains a permanent record and reference point which can be referred to at any time in the future. 


Malcolm (@Blessed Weather) recently produced an excellent post on hurricanes (see higher up on this page) and looked at the various relationships and impacts of some the teleconnections on this violent phenomena. This included the impacts from the ENSO (El Nino Southern Oscillation, El Nino and La Nina), the QBO (Quasi-Biennial Oscillation), the AMO (Atlantic Multi-Decadal Oscillation), SST (Sea Surface Temperatures) and the NAO (North At;antic Oscillation).  Malcolm and I, as well as Zac (@Snowy Hibbo) have been very busy adding links to papers on the "Teleconnections Research Portal". This now has an extensive range of papers on teleconnection related topics. Although some of the papers are pretty technical and, perhaps, for those at a more advanced level, many of the papers are for "early learners" and include  some simple definitions, fact sheets and guides. We are all learners at various points on the spectrum.  I feel that I still have a lot to learn about many aspects of teleconnection science and even the specialists have some weaker areas in this vast subject. We hope that many more members will join us on this learning curve.  Everyone is invited to participate - perhaps a comment or a query on a paper (we have an "Interactive Area" in the portal as well as the usual "reply to topic" option below each paper listing) or a post on this thread. 


I shall now pick up where Malcolm left off with a review of some more papers and I shall include several on tornadoes as well as more on hurricanes.  The links below are all to the portal and the abstract or summary of each paper.  From there you will find a quick link to the full paper, topic or guide.  Just click on titles below. 


1.   Hurricane Structure


Malcolm already listed this link but I want to emphasise how useful this is for learning so much about the basics. I copy my short review below:


This is one of a number of simple fact sheets produced by "Science & Society". This one looks at the structure of a mature hurricane with some excellent annotated diagrams.There is a fascinating part describing the eye wall and it explains how multiple walls form, expand, contract and decay and can be responsible for winds temporarily easing before strengthening again during the life of the storm. It describes one of the largest tropical cyclones "Typhoon Tip" in the north-west Pacific in 1979 which had a diameter of over 1,350 miles and covered an area equivalent to the entire western half of the US!  This is an excellent guide for learners and there are links to other parts of this site. 


Here's one of a number of excellent diagrams:   



List of Further Fact Sheets About Hurricanes on the Same Science & Society Site:

  • Primary Circulation 
  • Hurricane Movement
  • Hurricane Life Cycle
  • Hurricane Genesis: Birth of a Hurricane
  • Hurricane Development: from Birth to maturity
  • Hurricane Decay: Demise of a Hurricane
  • Interaction Between a Hurricane and the Ocean
  • Interaction Between a Hurricane and the Land
  • Variability of Hurricane Activity
  • Hurricanes and Climate
  • Hurricane Observations
  • Hurricane Forecasting and Modelling
  • Hurricane Katrina Case Study - a Category 5 storm that made US landfall on August 28th, 2010 with huge impacts, flooding 80% of New Orleans to a depth up to 15 feet. 

Once you have entered this site, there are fast links between each topic and a whole lot more there too.  It's well worth a thorough examination.


2.   About the Atlantic Multidecadal Oscillation (AMO)


Again Malcolm reviewed a paper on the AMO.  I found this simple guide and here's my review:


This is one of NOAA's excellent guides. It tells us all about the AMO and explains that it's currently its warm phase (since 1990) which can last from 20 to 40 years. This oscillation can be traced back for over 1,000 years and is not related to global warming. During the warm phase evidence shows that the AMO affects the frequency and severity of Atlantic hurricanes with over twice the number of major events compared to the cool phase. The AMO also strongly impacts on the climate of central and southern Florida with greater rainfall in the warm phase and more frequent droughts and wildfires during its cool phase.   


Here's a list of the what this fact sheet covers:


What is the AMO?

How much of the Atlantic are we talking about?

What phase are we in right now?

What are the impacts of the AMO?

How does the AMO affect rainfall and droughts?

How does the AMO affect Florida?

How important is the AMO when it comes to hurricanes - in other words - is it one of the biggest drivers? Or Just a minor player?

Does the AMO influence the intensity or the frequency of hurricanes (which)?

If the AMO affects hurricanes - what drives the AMO?

Can we predict the AMO?

Is the AMO a natural phenomenon, or is it related to global warming?


3.   What is an African Easterly Wave ? 


This is another simple fact sheet and here's my review:


This is one of a number of simple fact sheets produced by "NOAA". This one looks at the "Easterly Waves" which are born out of disturbances over North Africa and can move westwards across the tropical North Atlantic. These waves lead to the development of about 60% of all tropical storms and hurricanes but account for 85% of all major hurricanes. This is an excellent guide for learners. 





4.    The Dynamics of ENSO–Atlantic Hurricane Teleconnection: ENSO-Related Changes to N African–Asian Jet Affect Atlantic Basin Tropical Cyclogenesis


Yet another topic that Malcolm focused on was the relationship between ENSO and hurricanes.  I found this fascinating paper and here's the abstract:


The nature of the teleconnection linking ENSO variability with Atlantic basin tropical storm formation is investigated. Solutions of the linearized barotropic vorticity equation forced with August–October El Niño event divergence produce upper-tropospheric vorticity anomalies over the Sahel and at the mouth of the North African–Asian (NAA) jet over the tropical Atlantic. These responses are similar in magnitude and orientation to observed ENSO vorticity variability for this region.

Further investigation reveals that the vorticity anomalies over the subtropical Atlantic develop primarily in response to very low wavenumber, westward-propagating stationary Rossby waves excited by El Niño–related convective activity over the equatorial Pacific Ocean. However, the dynamics of this teleconnection change as the Atlantic basin hurricane season progresses. In August and September the response is dominated by the westward-propagating stationary Rossby waves that alter vorticity within the NAA jet and to its south. The upper-tropospheric nondivergent zonal wind anomalies produced by these vorticity anomalies are similar in pattern to observed zonal wind and vertical zonal wind shear anomalies, which suppress Atlantic basin tropical cyclogenesis.

By October, eastward-propagating signals also develop over the tropical Atlantic Ocean in response to El Niño conditions. Over the main development region of Atlantic basin tropical cyclogenesis, these eastward-propagating Rossby waves appear to destructively interfere with the vorticity changes produced by the westward-propagating Rossby waves within the NAA jet. In addition, the NAA jet has shifted south by October. Consequently, the resultant upper-tropospheric nondivergent zonal wind perturbations for October are weak and suggest that ENSO should have little effect on rates of Atlantic basin tropical cyclogenesis during October. Statistical analyses of monthly ENSO-related changes in Atlantic basin tropical storm formation support this hypothesis.


What I found of particular interest was how the responses and impacts differed as the hurricane season progressed.  The different responses to El Nino, La Nina and ENSO neutral conditions are analysed.  These charts are plots of where tropical storm evolutions began during El Nino and La Nina years between 1864 and 2002:




5.    Have Increases in CO2 Contributed to the Recent Large Upswing in Atlantic Basin Major Hurricanes Since 1995?


There have been quite a few papers in recent years examining the impacts of global warming and climate change on the length, intensity and frequency of storms during the Atlantic hurricane season. As with other papers that embrace this subject, I always endeavour to read them with caution, taking a neutral and non-political view. Some papers are very slanted and biased towards one side of the debate or the other.  I feel that we need to consider the evidence by looking at the facts and not at some of the controversial statements. This paper examines the changes in major hurricane activity by comparing the 1970-1994 period to the 1995-2010 period and takes account of the multi-decadal variations in the Atlantic. It considers the increases in CO2 emissions and human influences but also what "might" be more natural variations in sea surfaces temperatures and also salinity anomalies.  It concludes that the increased major hurricane activity may be due to the more natural variations and not to increases in CO2. There have been more recent papers on this subject and I (we or any other member) should attempt to sift through them and we can add the suitable ones to the Research Portal. We shall continue to search for factual and evidence based papers to provide the "balance" required in these sensitive areas. This is definitely an area where many members might like to contribute to.  More on this paper:



A large increase in Atlantic basin major hurricane activity has occurred since 1995 in comparison to the prior 25-year period of 1970–1994. It has been tempting for many who do not have a strong background in hurricane knowledge to jump on this recent 16-year increase in major hurricane activity as strong evidence of a human influence on hurricanes. The last 16-year active major hurricane period of 1995–2010 has, however, not been more active than a number of earlier periods of similar length when the Atlantic Ocean circulation conditions were similar to what has been observed since 1995. These earlier active conditions occurred when atmospheric CO2 amounts were lower than they have been in recent years.

The Atlantic basin undergoes large multi-decadal variations in hurricane activity, particularly major hurricane activity. These variations are largely a result of alterations in the strength of the Atlantic Ocean's thermohaline circulation (THC) which we hypothesize to be driven by Atlantic Ocean salinity variations. This paper discusses how the Atlantic THC acts to bring about strong multi-decadal modulation to Atlantic hurricane activity.

Publisher Summary:

It is not possible to directly measure the strength of the thermohaline circulation (THC). But its strength can be inferred from proxy measurements of the North Atlantic SST and salinity anomalies (which are directly related to each other) minus the sea level pressure anomaly (SLPA) over the broad Atlantic (0–50°N; 70°W–10°W). When the THC is strong, the Atlantic atmospheric and oceanic subtropical gyres are weaker than normal. When the Atlantic THC is weaker than average, the gyres are stronger than normal. With regards to multidecadal variations of Atlantic major hurricane activity, it is possible to give a sequence of physical arguments for how a year or a multidecadal period with a stronger than normal THC will have tropical Atlantic conditions associated, which are more favorable for Atlantic basin major hurricane activity. Among these conditions are positive tropical Atlantic sea surface temperature anomaly, lower tropical Atlantic SLPAs, weaker trade winds, and smaller values of tropospheric vertical wind shear. There is no evidence that Atlantic hurricane activity is significantly impacted by CO2 increases or by global mean surface temperature changes. This myth should be put to rest. It is the natural variability of the Atlantic's meteorological parameters that one must be concerned about.


Here's the table of contents for this paper:




Here's a small selection of the excellent charts and diagrams from the paper:











6.    How are Hurricanes Different from Tornadoes


Before I move onto tornadoes, there are a couple of simple fact sheets which look at the links and differences between hurricanes and tornadoes.  Here's my review:


This is one of a number of simple fact sheets produced by "Science & Society". It contains a table comparing these two weather hazards which can have severe impacts on human life. It shows how different these two phenomena are in terms formation, longevity, size, frequency, how strong their winds are, extent of impacts and how far in advance they can be forecast. The only association is that tornadoes can form within the circulation of a hurricane, usually in the rain bands spiralling around the hurricane but more rarely they have been observed within the eye wall. This is an excellent guide for learners and there are links to other parts of this site. 




7.    How Do Hurricanes Spawn Tornadoes?


Although the main conditions that create hurricanes and tornadoes are very different (see the comparisons above), the majority of hurricanes do actually spawn tornadoes.  Here's my review: 


This simple guide explains how (usually) relatively weak tornadoes (F2 and below) are spawned in the circulation of most hurricanes. It was first published in 2013 but then updated in 2017 to include the impact of Hurricane Irma on Key West and western Florida coast as a category 4 major hurricane on 8th September, 2017. There are links to a full account of this hurricane as well as photographs. This is an excellent guide for learners and there are links to other parts of this site. 


8.     All About Tornadoes - A Fact Sheet 


Still on simple fact sheets, I found this superb one produced by National Geographic. Here's my review:


This excellent fact sheet describes how a tornado is formed, their characteristics and the types of weather associated with them. It contains all sorts of fact and figures about them and is well illustrated with several impressive videos and a series of spectacular photographs. It shows what type of damage they can do and explains how they are forecast.  A superb read and a really useful learner's guide.


....and here's just one of the photographs:




There is so much to view on this site;  here's just a small sample:


  • A tornado forms when changes in wind speed and direction create a horizontal spinning effect within a storm cell. This effect is then tipped vertical by rising air moving up through the thunderclouds.
  • The meteorological factors that drive tornadoes make them more likely at some times than at others. They occur more often in late afternoon, when thunderstorms are common, and are more prevalent in spring and summer. However, tornadoes can and do form at any time of the day and year.
  • Tornadoes' distinctive funnel clouds are actually transparent. They become visible when water droplets pulled from a storm's moist air condense or when dust and debris are taken up.
  • Funnels typically grow about 660 feet (200 meters) wide.
  • Tornadoes move at speeds of about 10 to 20 miles (16 to 32 kilometers) per hour, although they've been clocked in bursts up to 70 miles (113 kilometers) per hour. Most don't get very far, though. They rarely travel more than about six miles (ten kilometers) in their short lifetimes.
  • Tornadoes are classified as weak, strong, or violent storms. Violent tornadoes comprise only about two percent of all tornadoes, but they cause 70 percent of all tornado deaths and may last an hour or more.
  • People, cars, and even buildings may be hurled aloft by tornado-force winds—or simply blown away. Most injuries and deaths are caused by flying debris.
  • Tornado forecasters can't provide the same kind of warning that hurricane watchers can, but they can do enough to save lives. Today the average warning time for a tornado alert is 13 minutes. Tornadoes can also be identified by warning signs that include a dark, greenish sky, large hail, and a powerful train-like roar.


9.   Tornado Frequency in the United States Related to Global Relative Angular Momentum


Of course this is a "more technical" thread and some of the papers cover more advanced parts of the subject. Malcolm found this excellent paper recently which was published in 2016 and we have been in touch with one of the authors, Vittorio A. (Victor) Gensini who produces some of the current AAM and GWO charts (various references in a number of posts on this thread).  This paper assesses US tornado frequency in relation to certain phases of the GWO (Global Wind Oscillation). Here's the abstract:


Global relative angular momentum and the first time derivative are used to explain nearly an order of magnitude of the variability in 1994–2013 U.S. boreal spring tornado occurrence. When plotted in a phase space, the global wind oscillation (GWO) is obtained. This global index accounts for changes in the global budget of angular momentum through interactions of tropical convection anomalies and extratropical dynamics including the engagement of surface torques. It is shown herein that tornadoes are more likely to occur in low angular momentum base states and less likely to occur in high angular momentum base states. When excluding weak GWO days, a maximum average of 3.9 (E)F1+ tornadoes per day were found during phase 1. This decreases to a minimum of 0.9 (E)F1+ tornadoes per day during phase 5. Composite environmental analysis suggests that increases/decreases in tornado occurrence are closely associated with anomalies in tropospheric ingredients necessary for tornadic storms. In addition, tornado frequency days exceeding the 90th percentile are shown to be favored when the global relative angular momentum budget and first time derivative are negative (GWO phases 1 and 2), as are significant tornado events [(E)F2+]. Implications for using GWO as a predictor for tornado forecasting are also discussed.


This is one of a number of charts showing the frequency of tornadoes in the GWO phases - 5.1 per day in phase 1 and down to 2.6 per day in phase 5.   We have shown the GWO phase charts in a number of posts on this thread - most recently in Zac's excellent post immediately above this one. So, please refer to that chart when you read this full paper. Other charts show the frequency of stronger tornadoes and the geographical spread across North America. 



The paper ends with this:


Discussion and summary:

The explanatory power of GWO during boreal spring in the United States is significant. Its use as a forecast tool for subseasonal tornado occurrence in the United States appears promising, but this study does not address such a question. Rather, the purpose here is to show the relationship wherein the frequency of tornado occurrence is significantly enhanced during periods when the time tendency of MRis negative. Future work will investigate the potential utility of GWO as a tornado frequency predictor. However, a forecaster should note periods when the GWO becomes active and increases amplitude (phases 4, 5, and 6) via positive mountain and frictional torque, and increasing convection near the international date line (related to the MJO). This forces a stronger Hadley cell circulation, causing anomalous fluxes in the tropical meridional tropospheric wind component. As air is displaced poleward, it moves closer to the earth’s axis of rotation, thus causing increases in the zonal wind component due to the conservation of angular momentum. An increase in Northern Hemisphere westerly momentum results, which produces an extension of the polar jet stream over the Pacific Ocean. This gives rise to positive MR anomalies, characteristic of GWO phases 5 and 6. It is the decreasing tendency of MR, and subsequent amplification of the polar jet stream over the Pacific Ocean (phases 8, 1, and 2) that favors synoptic weather patterns supportive of tornadoes east of the U.S. Rocky Mountains. These synoptic weather patterns include a midtropospheric trough in the western United States and a poleward flux in surface moisture across the Great Plains. A complete GWO circuit (counterclockwise orbit in phase space) can range from a broad range of 15–80 days (Weickmann and Berry 2009).

Monitoring and prediction of U.S. tornado frequency using the GWO will only be as skillful as the component calculations comprising MR. Essentially, forecasting a GWO orbit will be contingent upon the predictability of the MJO and the engagement of the surface tourques that contribute to the global AAM budget. As our skill in predicting ENSO, MJO, and various other teleconnections increase, so too will our ability to capture all contributing components using the GWO framework. Thus, we recommend further analysis and prediction of the GWO if subseasonal forecasting of U.S. tornado occurrence is desired. We note, however, there will be no one magic index or parameter that will solve the complex interactions between components of our climate system in order to give extended lead time of tornado frequency. Instead, subseasonal forecasts for severe weather should understand that there are numerous physical processes involving multiple time and space scales that dictate where/when favorable conditions emerge for enhanced tornado frequency. This will ultimately allow forecasters to begin moving beyond the current one week limitation of U.S. tornado frequency prediction.


Overall this is an original and fascinating piece of research and seems very likely to assist general tornado forecasts - when they will be much more or much less likely/frequent and for several weeks in advance.  The authors state that considerable further research is required.  I will need to read up much more on this before I could contemplate a full post on this specific topic. We are hoping that Victor Gensini (as well as Ed Berry - see my review of his brilliant GSDM presentation several posts above this one) will contribute directly on this thread in due course.


Concluding Comments:


I have reviewed a number of hurricane and tornado papers and these and many others are all listed in our Research Portal.  We are regularly adding further papers to the portal, so please keeping checking in.  Further reviews will appear on here from time to time, either individually or for a group of papers covering similar topics.  We do hope that more members will get involved on here as well as visiting the portal. Any feedback or comments will always be appreciated and, in particular, your own posts will be warmly received.  David :) 





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In this report I will look at the current state of the El Nino Southern Oscillation (ENSO) and the forecasts for the rest of this year. I'll include an overview of current sea surface temperatures (SSTs) in the Pacific and Atlantic Oceans and make some comments on the Atlantic and east Pacific hurricane/cyclone season.


Link to full weekly NOAA ENSO report (published on 25th June, 2018):


Here is a small selection of charts from the report with my comments (including on the hurricane season) below:


As forecast, the La Nina conditions have continued to weaken and we are currently in an ENSO neutral state with mostly (see below) slightly above average SSTs (sea surface temperatures) in the equatorial Pacific.  There is a 50% chance of SSTs continuing to rise during the summer with El Nino conditions developing during the fall (Autumn). These chances increase with the positive trend continuing towards the end of 2018 with a 65% chance of El Nino conditions developing - defined as 3 consecutive months with SST anomalies above +0.5c in the Nino 3.4 region (see below).



This is not quite a complete story across all the Nino regions of the equatorial Pacific as can be seen above. Nino 4, in the west, has been positive for the last 2 months and Nino 3.4 and 3, central and east/central, have been positive for the last month or so but Nina 1+2, far east, after rising during May have fallen back again during June (more on this below).



Pacific Ocean: SSTs on the "equator" are positive over most of the Pacific with just that very small patch (in Nino 1+2) close to the S American coast slightly below average. The tropical south Pacific SSTs are below average in the east and central parts and slightly above average over the western part. Further south there are large areas with above average SSTs, particularly in the west towards New Zealand. The tropical north Pacific has generally above average SSTs. In the simplest terms (as other factors are involved), this "may" favour slightly above average cyclone activity in the east Pacific and "perhaps" 1 or 2 of these making it across central America into the Gulf of Mexico (see below). Further north, apart from small areas of neutral to slightly below average SSTs in the centre and far north-west, most of the area is above average and in the west, towards Japan, as well as towards Alaska, substantially above average.


Atlantic Ocean: In the equatorial Atlantic there are slightly above average SSTs on the African side and neutral to slightly below average on the S American side.  In the tropical south Atlantic SSTs are slightly above average towards Africa and neutral to slightly below average towards S America. Further south there are large areas with above average SSTs particularly towards Argentina. The tropical north Atlantic has generally below average SSTs and substantially below off Africa. The Caribbean is neutral to very slightly below average but the Gulf of Mexico is well above average.  Again, in the simplest terms (as other factors are involved too), my view is that we "may" see a lower than average number of named tropical storms this year. Any that do form and track over the Gulf Of Mexico (including any east Pacific cyclones mentioned above) will have a good supply of above average SSTs which "may" lead to extending their life span and "might" favour several developing into more powerful hurricanes. Most of the major (category 4 and 5) hurricanes that develop (perhaps 80% to 90%) particularly in the second half of the season (late August onwards) are born from disturbances coming out of equatorial Africa and crossing the equator on the "African Easterly Wave". My view is that their development is likely to be inhibited as they will have to cross that area of below average SSTs before they reach the Caribbean and Gulf of Mexico.  I go into this again later in this post.


Please note that we have been busy adding many more papers into the Teleconnections Research Portal  (click on those words for a direct link). During the last 2 weeks I have been focusing on papers on the "African Easterly Wave", the "AMO" (Atlantic Multi-decadal Oscillation), "Hurricanes" and "ENSO".  There is a good mix from learning guides through (thru) to more advanced papers and a number of video presentations.  Some papers were published in the last few months.  We will be reviewing a good number of these on this thread in the coming months. I believe that Malcolm @Blessed Weather is planning to do a post on the AMO shortly.  I have seen slightly conflicting views on the current hurricane season (some of these vary from mine) and with good reason, with various "special factors" involved. Apart from the state of ENSO and SSTs, we have the AMO trending steadily towards its negative phase (still very slightly positive). These conflicting views extend into some of the recent papers. I shall be fascinated to read Malcolm's post.


Back to the north Atlantic Ocean - further north, there is a large area of well above average SSTs extending from The Azores to the eastern US seaboard. There is an area of substantially above average SSTs surrounding the UK and also in the Mediterranean.  It was only 2 months ago that the UK saw well below average SSTs following two very cold spells resulting from the SSW (Sudden Stratospheric Warming) and a very late start to Spring.  Much of western Europe, southern Europe and the UK are in the middle of a prolonged spell of hot weather.  Meanwhile, the north-west Atlantic has a large area of below average SSTs. 


Indian Ocean: There are large areas of below average SSTs in the equatorial Indian Ocean with slightly positive anomalies further north and more substantially average above further south.



The table above relates solely to the Nino 3.4 region. The last quarter to the end of May shows the mean SSTs moving out of the La Nina state and into ENSO neutral conditions (-0.5c to +0.5c) and with the higher figures in June the trend is continuing, in line with recent and current forecasts. 



The forecast chart above shows the probable steady trend through neutral to El Nino during the second half of 2018. 



Of course, it's not all about NOAA/CPC and one set of forecast figures.  The chart above shows the forecast from 18 models. None show La Nina conditions and only 3 (2 do not go for the full period) show neutral conditions - 1 slightly below average and 2 nearer the +0.5c level, both having briefly shown El Nino conditions. All the others go for El Nino conditions with anomalies between around +0.7c and +1.5c by the end of winter 2018/19.



Another clue to near term and future trends in SSTs is to consider sub-surface temperatures.  The charts above show that almost all of the equatorial Pacific (except that narrow band in the far east adjacent to the S American coast) have been seeing positive sub-surface temperature anomalies. In many parts values are strongly positive and the trend has remained positive for the last 2 months. With only marginal cold upwellings in the far east and continuing sub-surface warming predicted more generally, this is a strong indication of a movement towards El Nino conditions during the coming months.  



As this is a US forum I show NOAA's US current and forecast charts (more details in their weekly report). The last month has seen temperatures generally above or well above average with slightly below average conditions in the west and nearer normal conditions in the far north-east. It was particularly dry in the south-west, much of the south and the north-east but with normal or wetter than average conditions in other parts, mostly due to convective precipitation.



Looking ahead to the next quarter, almost all the US is forecast to see above average temperatures with the highest anomalies predicted to be in the west, the far north-east and Alaska.  Most parts are expected to see precipitation close to average - perhaps slightly drier than normal in the far south and north-west and slightly wetter than average in the south-west, the far east and Alaska. So, much of the US is likely to join much of Europe in a generally warmer than average summer with some parts possibly seeing considerably warmer conditions.  


NOAA also produce an excellent monthly diagnostic discussion and this backs up some of what I have outlined above.

Link to NOAA - ENSO Monthly diagnostic Discussion published on 14th June, 2018:


To get a better feel for the warming trend in the equatorial Pacific, it is useful to look at animated charts. Remember that the equatorial zone moves northwards in the northern hemisphere summer. It is not a smooth trend but the area with warm or very warm SSTs has expanded, particularly in the west (1st chart below) and there are weaker negative and stronger positive anomalies (2nd chart below). 


 sstanim.gif   sstaanim.gif

Source Link:

Please note that to provide the animations for the two charts above, I had to use the "copy image address" feature and they are likely to "auto update" within a week or two and my comments relating to them may become slightly out-of-date.  


Those charts were up to 20th June at the time of writing this post (on 30th June).  I've found a very useful recent chart with tropical Atlantic SSTs as at 29th June, 2018 (below):


This helps to illustrate my point about a weaker than average hurricane season.  Remember the critical SST value for the further development and the sustaining of tropical storms/hurricanes is 27c. Above that value and the conditions are conducive to development, particular if they are widespread. Below that value and storm formation is suppressed. The Gulf of Mexico is generally above 27c - nearer 28c to 29c but the Caribbean is generally just below 27c - nearer 26c.  Along the equator coming out of Africa there are patches of 27c to 28c but more generally nearer 26c to 27c - so marginal conditions right now.  At 10N to 20N, the key area that the African easterly waves have to move across to reach the Caribbean,  values are almost entirely below or well below 27c. They are mostly 24c to 26c and down to 22c or even lower slightly further north.  Yes, the disturbances coming out of Africa can remain farily weak while they cross the Atlantic but they almost need to complete their entire crossing until they hit any 27c + SSTs.  So this is why I said very few major hurricanes and below average minor ones.  There are "no" tropical storm advisories in the Atlantic for the next 5 days. 


As I mentioned earlier, there is that wide area of 27c to 29c SSTs in the tropical eastern Pacific and if any tropical storms manage to track across central America to reach the Gulf of Mexico then they might grow into major hurricanes.  Most of the east Pacific tropical storms and cyclones that come close to the western Mexican coast tend to move off in a north-westerly direction.  There are a couple of disturbances there right now:


Source Link:

Tropical Depression Emilia Public Advisory

WTPZ31 KNHC 301431

Tropical Depression Emilia Advisory Number  12
NWS National Hurricane Center Miami FL       EP062018
800 AM PDT Sat Jun 30 2018


LOCATION...17.7N 119.2W

There are no coastal watches or warnings in effect.

At 800 AM PDT (1500 UTC), the center of Tropical Depression Emilia
was located near latitude 17.7 North, longitude 119.2 West. The
depression is moving toward the west-northwest near 12 mph (19
km/h), and this general motion is expected to continue for the
next day or two.

Maximum sustained winds have decreased to near 35 mph (55 km/h) with
higher gusts. Emilia is forecast to degenerate into a remnant low
later today.

The estimated minimum central pressure is 1004 mb (29.65 inches).


Next complete advisory at 200 PM PDT.

Forecaster Avila

Source Link:


Overall we need to keep a close eye on those SSTs but I feel that US members and all hurricane followers should focus far more on the eastern Pacific than the Atlantic during the remainder of the 2018 season.


I shall post a plug for this report on the Hurricane thread but it does belong here as I am dealing more with ENSO and the teleconnections.  David :) 


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New Source for Access to AAM and Torque Data

In a recent post (further up this page) entitled "What is the GSDM and how does it help with subseasonal weather forecasts? - A Review of This Presentation" I explained that I had contacted Ed Berry, who, along with Dr Klaus Weickmann, developed the GSDM while they worked at NOAA from the late 1990s until around 2015.  Klaus has retired but Ed is still active. I highly recommend reading and viewing his recent presentation to anyone interested in learning more about aam (angular momentum), the gwo (global wind oscillation) and frictional and mountain torques. 


Since then, several of us have been in touch with Ed on related matters. Last month WDT finally withdrew all access to their aam and torque data which was the only freely available source of this vital information. I asked Ed about this and, thankfully, he has a friend who produces this data. He provided us with a link to his data site and we are extremely grateful for this. Here are the access details to sign in:


Link to site:

User ID:            gsdm01

Password:       gu3st#1


When you are in there you will see this contents page (this one was from 1st July, 2018) which is updated daily with around the usual 2 day time lags:



Climate Products


Monitoring of Global Atmospheric Angular Momentum (AAM) Budget

NCEP-NCAR Reanalysis



Please note that the links in the contents table above will only work for up-to-date data once you have accessed the site (as shown above).


For those that are familiar with the previous data, you can see that there is access to far more data than we were able to obtain from WDT. The plots include quarterly and annual data for aam, the torques and other charts such as on gravity wave drag.  There is archive data, charts and tables with plots going back to 1958. The data files are "zipped" and if you do not have the software to open them you will need to download it. I just used a  compatible zip extraction

and compression programme for my PC (I'm still using windows 7!) which is safe and one of those that is recommended and free to use. Others are available.

Here's a link to the PeaZip site download page:


Many of the plots, charts and statistics will be regularly used by posters on this thread.


David :) 

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This is great, David! Thank you for gaining access to these absolutely integral data. I know, for me, I utilize AAM/torques fairly heavily in MR winter forecasting, so this is a major help.

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Negligible change from the last update (May), with the average of all forecasts still going for a transition to weak El Nino conditions late summer/early fall:


ENSO Model Predictions at July2018.jpg


"Climate model ensemble average calls for borderline weak El Nino conditions for peak of Atlantic hurricane season (August-October), with potential for weak to moderate El Nino during the winter of 2018/19." 

Philip Klotzbach.


Phil Klotzbach is a Research Scientist in the Department of Atmospheric Science at Colorado State University specializing in hurricanes, so his interest in ENSO is related to its impact on the hurricane season. There are a number of papers in the Research Portal on this, but the following is very relevant:


Impacts of El Niño and La Niña on the hurricane season.
“El Niño favors stronger hurricane activity in the central and eastern Pacific basins and suppresses it in the Atlantic basin. Conversely, La Niña suppresses hurricane activity in the central and eastern Pacific basins and enhances it in the Atlantic basin.
These impacts are primarily caused by changes in the vertical wind shear, which refers to the change in wind speed and direction between roughly 5,000-35,000 ft. above the ground. Strong vertical wind shear can rip a developing hurricane apart, or even prevent it from forming.”


Research Portal link:ño-and-la-niña-on-the-hurricane-season/

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