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I've wanted to post in this thread for a while, but have been sidetracked by the actual weather following the SSW, but with the current rain, drizzle and generally rubbish weather, I'm taking a break from the MOD!  I think this thread is excellent and look forward to following it avidly.  
I've tried to read up on teleconnections, particularly the GWO and AAM, but feel there are still some major gaps in my understanding that maybe you folks could help with.  So two questions for today:
1. The phrase 'seasonal wavelength changes' is one I've seen regularly in posts relating to teleconnections.  I'm unsure what this means, although I assume it relates to the meandering of the jet stream in some way. So could anyone please provide an explanation of:  the wavelength of what is changing, how does it change, why does it change, and how might that impact the UK at various times of year?
2. A lot of discussion I've read has been related to winter.  I'd like to know what teleconnections can tell us about summer, I know the strat is out of play, but what can give an indication of summer weather patterns a few weeks in advance?
Thanks in advance and very best regards.
Mike

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I just wanted to say that I have recently taken on some additional business commitments which will take up the small amount of free time that I have available for an extended period. I will now only be able to post very occasionally and perhaps not at all during the next few months. Needless to say, I will not have any time to develop this learning thread as I had wished to. I apologise to anyone who was expecting to see greater activity on here. I hope that others will continue to contribute to and support this thread with questions and answers. Perhaps someone might like to respond to @Mike Poole and his queries in the post just above this message. This is exactly what this thread is intended for.

David. 

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4 minutes ago, Bring Back1962-63 said:

I just wanted to say that I have recently taken on some additional business commitments which will take up the small amount of free time that I have available for an extended period. I will now only be able to post very occasionally and perhaps not at all during the next few months. Needless to say, I will not have any time to develop this learning thread as I had wished to. I apologise to anyone who was expecting to see greater activity on here. I hope that others will continue to contribute to and support this thread with questions and answers. Perhaps someone might like to respond to @Mike Poole and his queries in the post just above this message. This is exactly what this thread is intended for.

David. 

Good luck with these extra commitments :) 

I will attempt to do the occasional post, though as with you my time will be constrained when back studying next week. I will hopefully formulate a response to Mike in the upcoming days :) .

On a separate note, I will be transferring across a detailed update to the 'Hurricane Tutorial' written back in 2005 in preparation for the upcoming North Atlantic Hurricane Season. It should be fully updated and available on here within two weeks, anyone interested should occasionally check in the Hurricane Tutorial thread and possibly any new thread for the upcoming season where it will likely be added to. 

  

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On 4/3/2018 at 20:16, Mike Poole said:

I've wanted to post in this thread for a while, but have been sidetracked by the actual weather following the SSW, but with the current rain, drizzle and generally rubbish weather, I'm taking a break from the MOD!  I think this thread is excellent and look forward to following it avidly.  
I've tried to read up on teleconnections, particularly the GWO and AAM, but feel there are still some major gaps in my understanding that maybe you folks could help with.  So two questions for today:
1. The phrase 'seasonal wavelength changes' is one I've seen regularly in posts relating to teleconnections.  I'm unsure what this means, although I assume it relates to the meandering of the jet stream in some way. So could anyone please provide an explanation of:  the wavelength of what is changing, how does it change, why does it change, and how might that impact the UK at various times of year?
2. A lot of discussion I've read has been related to winter.  I'd like to know what teleconnections can tell us about summer, I know the strat is out of play, but what can give an indication of summer weather patterns a few weeks in advance?
Thanks in advance and very best regards.
Mike

Good Evening Mike :)  ,

Seasonal Wavelength Change : With regard to the notion of teleconnections, this relates (as you mentioned) to jet stream undulation/amplitude.  Winter is characterized through a high poleward temperature gradient, resulting in increased upper atmospheric zonal winds (Jet Stream). High velocity upper atmospheric winds rarely reflect themselves in a meridional (high amplitude) setup, partial reasoning at least why winter weather is dominated by interchangeable surface setups (Unsettled). In summer months, with the considerable weakening of the polar vortex the temperature gradient is far less pronounced, resulting in lower upper atmospheric zonal winds (Jet Stream). This can and usually translates to a more amplified pattern being seen in the upper winds. In short, summer is characterized by short wavelength (increased amplitude) jet stream (Slower Aswell) setups and this is reversed in winter months. 

A possible approach to this (for beginners), is to consider why blocked surface patterns gain so much interest in the winter period. It will have weak correlation with fanatical hopes of snowmageddon, but on a serious note it provides respite from the broad continuum of strongly zonal conditions. Wavelength changes can change more abruptly on reduced timescales, these being induced by changes in the global wind oscillation (GWO), MJO phases etc. 

An interesting line of thought, especially since the turn of the millennium regards an ever increasingly undulated jet stream in both winter & summer potentially related to arctic temperature sensitivity. Here are a few links to research papers for you : 

https://ams.confex.com/ams/94Annual/webprogram/.../Extended Abstract.pdf

http://iopscience.iop.org/article/10.1088/1748-9326/10/1/014005/pdf

Feel free to message me with any specific queries :) 

 

 

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22 hours ago, MattTarrant said:

Good Evening Mike :)  ,

Seasonal Wavelength Change : With regard to the notion of teleconnections, this relates (as you mentioned) to jet stream undulation/amplitude.  Winter is characterized through a high poleward temperature gradient, resulting in increased upper atmospheric zonal winds (Jet Stream). High velocity upper atmospheric winds rarely reflect themselves in a meridional (high amplitude) setup, partial reasoning at least why winter weather is dominated by interchangeable surface setups (Unsettled). In summer months, with the considerable weakening of the polar vortex the temperature gradient is far less pronounced, resulting in lower upper atmospheric zonal winds (Jet Stream). This can and usually translates to a more amplified pattern being seen in the upper winds. In short, summer is characterized by short wavelength (increased amplitude) jet stream (Slower Aswell) setups and this is reversed in winter months. 

A possible approach to this (for beginners), is to consider why blocked surface patterns gain so much interest in the winter period. It will have weak correlation with fanatical hopes of snowmageddon, but on a serious note it provides respite from the broad continuum of strongly zonal conditions. Wavelength changes can change more abruptly on reduced timescales, these being induced by changes in the global wind oscillation (GWO), MJO phases etc. 

An interesting line of thought, especially since the turn of the millennium regards an ever increasingly undulated jet stream in both winter & summer potentially related to arctic temperature sensitivity. Here are a few links to research papers for you : 

https://ams.confex.com/ams/94Annual/webprogram/.../Extended Abstract.pdf

http://iopscience.iop.org/article/10.1088/1748-9326/10/1/014005/pdf

Feel free to message me with any specific queries :) 

 

 

Many thanks for taking the time to reply to my question, @MattTarrant your answer is very clear, so I will know when reading posts about teleconnections in future what this refers to.

I will have a look at the papers that you have given links to.

Thanks again, much appreciated.

Mike

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On 4/12/2018 at 23:19, MattTarrant said:

Seasonal Wavelength Change : With regard to the notion of teleconnections, this relates (as you mentioned) to jet stream undulation/amplitude.  Winter is characterized through a high poleward temperature gradient, resulting in increased upper atmospheric zonal winds (Jet Stream). High velocity upper atmospheric winds rarely reflect themselves in a meridional (high amplitude) setup, partial reasoning at least why winter weather is dominated by interchangeable surface setups (Unsettled). In summer months, with the considerable weakening of the polar vortex the temperature gradient is far less pronounced, resulting in lower upper atmospheric zonal winds (Jet Stream). This can and usually translates to a more amplified pattern being seen in the upper winds. In short, summer is characterized by short wavelength (increased amplitude) jet stream (Slower Aswell) setups and this is reversed in winter months. 

A possible approach to this (for beginners), is to consider why blocked surface patterns gain so much interest in the winter period. It will have weak correlation with fanatical hopes of snowmageddon, but on a serious note it provides respite from the broad continuum of strongly zonal conditions. Wavelength changes can change more abruptly on reduced timescales, these being induced by changes in the global wind oscillation (GWO), MJO phases etc. 

An interesting line of thought, especially since the turn of the millennium regards an ever increasingly undulated jet stream in both winter & summer potentially related to arctic temperature sensitivity. Here are a few links to research papers for you : 

https://ams.confex.com/ams/94Annual/webprogram/.../Extended Abstract.pdf

http://iopscience.iop.org/article/10.1088/1748-9326/10/1/014005/pdf

 

Interesting answer, however wavelength and amplitude are separate distinct wave characteristics

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16 hours ago, Interitus said:

Interesting answer, however wavelength and amplitude are separate distinct wave characteristics

I never intended to directly define wavelength, my answer was portended to help Mike :) with his questions. 

Wavelength in it self is does not require much talk, I intended to discuss around the topic to help promote Mike's wider thinking. 

 

Edited by MattTarrant

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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. 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 presentation:    https://youtu.be/Cv5CblXbYuQ

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 to whet your appetite:

 ed1.thumb.PNG.ee988ae75134340f81506cdcd0d1661e.PNG ed2.thumb.PNG.2052a9e05041d9827fbc38002159df89.PNG ed3.thumb.PNG.e876fca5dee6eb0e19fab2b018398bb4.PNG ed4.thumb.PNG.9bdde0fbbd1637910371e0abeb510c42.PNG  ed5.thumb.PNG.abda5105d6c0099b520e0024f48882a0.PNG     

ed6.thumb.PNG.ec2206d2cd16dc4448ae84dbcc3e134f.PNG        ed7.thumb.PNG.dbd24ac556166052df3bcc606008cfff.PNG        ed8.thumb.PNG.c061ec7e1af78578145ff1684d87aadc.PNG       ed9.thumb.PNG.50828c66349244a751f5834d423d5428.PNG 

 

 ed10.thumb.PNG.67c67b5f4fb45c80801d3f3a0b3cda40.PNG       ed11.thumb.PNG.dd8cccec90b25f5868fad84db55af588.PNG      ed12.thumb.PNG.9809422e855029cc4bd4cfb4ee2b05a7.PNG        ed13.thumb.PNG.9a45c05d95672174dad1457f37fa389a.PNG

 

  ed14.thumb.PNG.5730a7db0c6700b5fbf2a07796301669.PNG  ed15.thumb.PNG.37af88d5a11c5ede7b566fee7d412d57.PNG    ed16.thumb.PNG.53324d4d5d40a9995230c319082e9932.PNG ed17.thumb.PNG.6dd6ffcbdc3af37fad9786e719716c79.PNG

 

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..

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H/t MV

Quote

The El Nino standing wave appears to have emerged with this most recent MJO passage across the Pacific. This is not a canonical east-based El Nino; it appears to be a basin wide event, which many call the Modoki. 2006 and 2009 are most recent events similar to today

El Nino influences the formation of low pressure systems over the Gulf Stream

Quote

Analysis of cyclone tracks and precyclogenesis flow conditions show us that El Niño can shift the preferred cyclogenesis position over the Gulf Stream which influences the cyclone's track across the North Atlantic.

Northern Europe is located at the end of the North Atlantic storm track and the low pressure systems that bring this area precipitation typically form above the Gulf Stream or at the southern tip of Greenland. A recent study published in the Journal of the Atmospheric Sciences, by Sebastian Schemm, Laura Ciasto, Camille Li and Nils Gunnar Kvamstø reveals how ENSO affects the formation of low pressure systems over the Gulf Stream area and consequently their tracks across the North Atlantic. The results are based on the analysis of the wintertime precyclogenesis flow across North America during three ENSO variants in an observation-constrained reanalysis dataset.
 

 

https://phys.org/news/2016-10-el-nino-formation-pressure-gulf.html

Edited by knocker

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Does anyone have any functioning AAM or torque monitoring sites anymore? All the usual suspects stopped working around June. Thanks. 

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Not sure whether this is the right topic for this - but what has been interesting lately, is the large amout of small-scale cut-off features that are located in/passing through the subtropics. These cut-off features are evident as small southward-extending 'drops' of low heights (green colours; equivalent to upper-level troughs). For this post I will mainly focus on the Atlantic sector, because that alone is already pretty interesting to consider :)

In the Atlantic, the cut-off lows have already been present from August onwards. These cut-off lows have been the breeding ground for several (sub-)tropical cyclones, like Debby, Ernesto, Joyce and Leslie. It is quite unusual that we see so many subtropical cyclones developing in the Atlantic from non-tropical origin. The extratropical re-intensificaiton of Lesile a few days ago was also aided by a southward-digging upper-level trough.

Likewise, in Europe there have also been some cut-off troughs already. One of these caused a subtropical cyclone to develop in the Mediterranean (the 'Medicane') that is active as of 28-9. In the next few days, yet another cut-off low will develop in the Mediterranean with the potential to take on some subtropical characteristics (see animation below).

ecmwf_z500_mslp_nhem_fh0-240.thumb.gif.f2c8ec18514403b0bd005ad7917dfb39.gif

Geopotential heights animation for 10 days out from the 28-09 run from ECMWF. Source: Tropicaltidbits

Looking at this flow pattern makes me wonder what is causing this unusual flow configuration. What I found is that we can find at least part of the answer to this puzzle in deviations from the jet stream. During August, the jet stream has been located unusually far to the north, as shown in the image below. That image shows the zonal (west-to-east) anomalies of winds at 300 hPa (8 km height) in August. At the latitutde of the UK, westerlies have been stronger than normal (implying a stronger jet). On the other hand, westerlies have been weaker than normal further south (implying a weaker jet). This corresponds to a northward displacement of the jet.

ESRL.thumb.png.d0ff75944b1e76b4786e38c68ef50a8a.png

Zonal (west-to-east) anomalies of winds at 300 hPa (8 km height) in August. The arrows illustrate the northward displacement of the jet stream. Source: ESRL NOAA

The pattern observed above matches the large amount of cutoff lows well - when the jet is located far to the north, troughs often dip far to the south and become cut-off from the main flow. If the jet were to be located more to the south, cut-off lows would be less frequent.

An interesting question is why we observe the northerly position of the jet and the large amount of cut-off lows in the Atlantic sector. Maybe this is linked to variations in the GWO? Since this pattern resembles the pattern of the summer to some extent (northerly position of the jet and +NAO), I suspect that any indicator must have been consistent already for most of the summer.

 

 

Edited by Vorticity0123

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On 25/09/2018 at 21:45, forecaster said:

Does anyone have any functioning AAM or torque monitoring sites anymore? All the usual suspects stopped working around June. Thanks. 

Hi, since the service provided through WDT was withdrawn there was a gap in this vitally important data. I've been in touch with Ed Berry, who along with Dr Klaus Weickmann (who retired 2 years ago)  developed the GSDM (see my post further up this page on that) and he told me that a friend of his still processes this data.  He has kindly provided a link to that site plus the access user name and password:

http://gsdmsolutions.com/~gsdm/clim/aam.rean.shtml

un = gsdm01

pw = gu3st#1

That will take you to this page where you'll find a lot more than just the ex WDT data.:

Monitoring of Global Atmospheric Angular Momentum (AAM) Budget

NCEP-NCAR Reanalysis

 

While I'm on this subject, it'll be timely to remind those interested of other similar links:

1. Nicholas Shiraldi - Albany for the GEFS AAM and GWO plots  - Note that this has not updated since June 28th 2018 due to ongoing GFS technical problems which we are assured will be resolved in due course (but no date given yet).

http://www.atmos.albany.edu/student/nschiral/gwo.html

 

2. SCW (South California Weather Notes) - this site provides a vast number of links although some are no longer available (such as the NOAA map room for AAM etc).  It is well worth exploring what's on offer, including some useful archive data.  For the GWO previous/current (but not forecast) plots go to the "Quick Link" near the top of the page and click on GWO/FNL.  The chart sometimes appears as a silhouette but will copy okay. This is the "final analysis" using GFS data.  Klaus Weickmann developed this as a way of checking the forecast output against what actually transpired. It is very useful as it doesn't appear to have the same strong -ve biases that GEFS are known to have. it is updated towards the end of each day.

http://www.sierraphotography.com/wxnotes/weatherlinks.htm

 

3. Dr Victor Gensini -  a research scientist in this field has been developing his own site during the last year.  It is still evolving but already has some extremely useful data.  Victor has been attempting to correct the GEFS -ve bias but his source data is suffering from the same technical faults - so not reliable right now. He also includes CFS output which has a rather +ve bias and allowances need to be made for that. He plans to process and add torque data in due course. Victor Gensini and Ed Berry are in regular contact with each other and may do some joint work providing that they can get the financial backing (always a problem in this area). 

http://atlas.niu.edu/gwo/

 

I have been away from NetWx for much of the summer and Malcolm @Blessed Weather and I (+ several others) have been very busy developing a Research Portal on a US forum. We plan to be active on NetWx and the US thread and may cross post on to both sites, especially for Teleconnection posts. We will be reviewing some excellent papers and presentations on both sites. For those interested in reading some of those papers, here's a link to the portal:

https://www.33andrain.com/forum/51-teleconnections-research-portal/

You can have temporary access as a guest and can view around 10 different papers in a 24 hour period. If you want to view more, you will need to register (which is free as they rely on voluntary donations). I suggest that you look at the comprehensive index. From there you can click on a title, that will take you to the abstract. After reading that, you can decide if you want to read the full paper and a direct link is provided. I had wanted to develop this portal on NetWx but it never got off the ground.  I'll be back on here within a few weeks and you'll see an increasing number of paper reviews.  David :)  

Edited by Guest
check links are working and correct typos

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On 29/09/2018 at 08:34, Bring Back1962-63 said:

https://www.33andrain.com/forum/51-teleconnections-research-portal/

You can have temporary access as a guest and can view around 10 different papers in a 24 hour period. If you want to view more, you will need to register (which is free as they rely on voluntary donations).

Or in Chrome for example, clear your cookies from the last hour, simples.

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Posted (edited)

During the Winter months I have helped Paul develop the Research section of the new-look Learning and Research area which can be located via the navigation bar at the top of every page. There's already many great research papers in there, but I thought from here on it would be a good idea to review on this thread any new papers that are added, so here goes. 

Relationship between the Quasi-Biennial oscillation and the Madden-Julian Oscillation.

After the erratic behaviour of the MJO (and erratic model forecasts of the MJO progression) over this last winter, the latest 2 additions to the library might be of interest. This conclusion from the research paper caught my eye:

"The MJOs in WQBO winters are often rapidly disorganised within a few weeks. This breakdown of MJO is not well captured by the S2S models, reducing the theoretical limit of MJO prediction."

Both a recent research paper (pub Mar 2019) and a scientific article (pub Feb 2019) have found that the winter strength and predictability of the MJO varies depending on whether the QBO is in easterly or westerly phase.

Here's the abstract from the article published on the Nature/Scientific Reports website. Click on the title to go to the full paper.

On the emerging relationship between the stratospheric Quasi-Biennial oscillation and the Madden-Julian oscillation
A strong relationship between the quasi-biennial oscillation (QBO) of equatorial stratospheric winds and the amplitude of the Madden-Julian oscillation (MJO) during the boreal winter has recently been uncovered using observational data from the mid-1970s to the present. When the QBO is in its easterly phase in the lower stratosphere, it favors stronger MJO activity during boreal winter, while the MJO tends to be weaker during the westerly phase of the QBO. Here we show using reconstructed indices of the MJO and QBO back to 1905 that the relationship between enhanced boreal winter MJO activity and the easterly phase of the QBO has only emerged since the early 1980s. The emergence of this relationship coincides with the recent cooling trend in the equatorial lower stratosphere and the warming trend in the equatorial upper troposphere, which appears to have sensitized MJO convective activity to QBO-induced changes in static stability near the tropopause. Climate change is thus suggested to have played a role in promoting coupling between the MJO and the QBO.

And here's part of the abstract from the research paper plus a chart showing model prediction skill (ECMWF leading the models). Click on the title to go to the full article.

Influence of the QBO on MJO prediction skill in the subseasonal-to-seasonal prediction models
Recent studies have shown that the Madden-Julian Oscillation (MJO) is significantly modulated by the stratospheric Quasi-Biennial Oscillation (QBO). In general, boreal winter MJO becomes more active during the easterly phase of the QBO (EQBO) than during the westerly phase (WQBO). Based on this finding, here we examine the possible impacts of the QBO on MJO prediction skill in the operational models that participated in the WCRP/WWRP subseasonal-to-seasonal (S2S) prediction project. All models show a higher MJO prediction skill during EQBO winters than during WQBO winters.

Model prediction skills: 2060161559_MJOmodelpredictionskill.thumb.jpg.99b3cec7150dd8c21f3c939bcbfc3381.jpg

 

Other research papers on this subject added to library. Click on title to go to the full paper.

QBO Influence on MJO Amplitude over the Maritime Continent: Physical Mechanisms and Seasonality

Stratospheric Control of the Madden–Julian Oscillation
 

Edited by Blessed Weather

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An initial 13 papers have been added to a new topic in the Research Library:

Rapid Cyclogenesis

The term is used to describe the rapid deepening of an extratropical (mid latitude) cyclonic low-pressure area where the rate of central sea-level pressure's deepening is greater than or equal to 1 hPa per hour, generally over a period of 12 hours or longer. Such developments are responsible for some of the worst storms to impact the UK. The UK media often refer to these developments as a “weather bomb”.

Below are some selected highlights from two research papers, but first of all an overview of a web based training resource also included in the library:

Rapid Cyclogenesis (website).

This comprehensive training resource is a collaboration by the Austrian Meteorological Institute (ZAMG) and Dutch and Finnish Meteorological Institutes (KNMI and FMI). It’s a good place to start for a broad understanding of the subject and uses diagrams and satellite images to help the reader understand how the development occurs, what meteorological drivers are behind it, how it is monitored and what weather events can follow.

Link to website: http://www.eumetrain.org/satmanu/CMs/RaCy/index.htm

The concurrence of atmospheric rivers and explosive cyclogenesis in the North Atlantic and North Pacific basins. (Dec 2017 paper)

This paper looks at the relationship between explosive cyclogenesis and the occurrence of atmospheric rivers. ARs are defined as a long, narrow, and transient corridor of strong horizontal water vapour transport that is typically associated with a low-level jet stream ahead of the cold front of an extratropical cyclone. They can typically be 500km wide and extend for thousands of km.

Abstract:
“The explosive cyclogenesis of extratropical cyclones and the occurrence of atmospheric rivers are characteristic features of a baroclinic atmosphere and are both closely related to extreme hydrometeorological events in the mid-latitudes, particularly on coastal areas on the western side of the continents. Using ERA-Interim reanalysis data for 1979–2011, we analyse the concurrence of atmospheric rivers and explosive cyclogenesis over the North Atlantic and North Pacific basins for the extended winter months (ONDJFM). Atmospheric rivers are identified for almost 80 % of explosive deepening cyclones.”

Link to full paper: https://www.earth-syst-dynam.net/9/91/2018/

Rossby wave‐breaking analysis of explosive cyclones in the Euro‐Atlantic sector. (June 2013 paper)

This paper looks at the relationship between explosive cyclogenesis and the occurrence of Rossby Wave-breaking. A RW is a large horizontal atmospheric wave that is associated with the meandering polar-front jet (PFJ) stream and separates cold polar air moving away from the Pole and warm tropical air moving away from the Equator. RWs in the Earth's atmosphere are easy to observe as typically 4 to 6 large-scale meanders of the PFJ. The deviations of the PFJ around masses of cold or warm air mark out low and high pressure systems that are responsible for day-to-day weather patterns at mid-latitudes.

Abstract:
“The two‐way relationship between Rossby wave‐breaking (RWB) and intensification of extratropical cyclones is analysed over the Euro‐Atlantic sector. In particular, the timing, intensity and location of cyclone development are related to RWB occurrences. Results show that explosive cyclogenesis over the North Atlantic (NA) is fostered by enhanced occurrence of RWB on days prior to the cyclone's maximum intensification. Under such conditions, the eddy‐driven jet stream is accelerated over the NA, thus enhancing conditions for cyclogenesis.”

Link to full paper: https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/qj.2190

The other papers in the Rapid Cyclogenesis Library listing can be found here.

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New research just been published looking at recent extreme weather in North America and Europe. The role of climate change is discussed, although the paper concludes that "Further research is required to fully understand the combination of factors that trigger these observed wave events".

Here's the press release 29/04/2019:

Summer extremes of 2018 linked to stalled giant waves in jet stream
Record breaking heatwaves and droughts in North America and Western Europe, torrential rainfalls and floods in South-East Europe and Japan - the summer of 2018 brought a series of extreme weather events that occurred almost simultaneously around the Northern Hemisphere in June and July. These extremes had something in common, a new study by an international team of climate researchers now finds: the events were connected by a newly identified pattern of the jet stream encircling the Earth. The jet stream formed a stalled wave pattern in the atmosphere which made weather conditions more persistent and thus extreme in the affected regions. The same pattern also occurred during European heat waves in 2015, 2006 and 2003, which rank among the most extreme heatwaves ever recorded. In recent years, the scientists observed a clear increase of these patterns.

Link to full press release: https://www.pik-potsdam.de/news/press-releases/summer-extremes-of-2018-linked-to-stalled-giant-waves-in-jet-stream

And the full research paper 26/04/2019:

Extreme weather events in early summer 2018 connected by a recurrent hemispheric wave-7 pattern
The summer of 2018 witnessed a number of extreme weather events such as heatwaves in North America, Western Europe and the Caspian Sea region, and rainfall extremes in South-East Europe and Japan that occurred near-simultaneously. Here we show that some of these extremes were connected by an amplified hemisphere-wide wavenumber 7 circulation pattern. We show that this pattern constitutes an important teleconnection in Northern Hemisphere summer associated with prolonged and above-normal temperatures in North America, Western Europe and the Caspian Sea region. This pattern was also observed during the European heatwaves of 2003, 2006 and 2015 among others. We show that the occurrence of this wave 7 pattern has increased over recent decades.

Link to full research paper: https://iopscience.iop.org/article/10.1088/1748-9326/ab13bf#erlab13bfapp3

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Posted (edited)

UK ‘stuck’ weather patterns due to Global Warming and slow moving Rossby Waves?

With late Spring/early Summer 2019 in the UK stuck in a very wet pattern and comparisons made with 2012, a quick look at further research identifying the causes. First of all, it's worth noting that back in 2012 the scientific evidence to confirm the theory was only just starting to appear, as this 2012 BBC report called Why, oh why, does it keep raining? suggests: https://www.bbc.co.uk/news/science-environment-18783422

So to add to the findings of the research paper Extreme weather events in early summer 2018 connected by a recurrent hemispheric wave-7 pattern reviewed in my post above, I’ve just added another paper to the Netweather Research library (here) titled Evidence linking Arctic amplification to extreme weather in mid‐latitudes. Here are the conclusions of the research:

In summary, the observational analysis presented in this study provides evidence supporting two hypothesized mechanisms by which Arctic amplification – enhanced Arctic warming relative to that in mid‐latitudes – may cause more persistent weather patterns in mid‐latitudes that can lead to extreme weather. One effect is a reduced poleward gradient in 1000‐500 hPa thicknesses, which weakens the zonal upper‐level flow. According to Rossby wave theory, a weaker flow slows the eastward wave progression and tends to follow a higher amplitude trajectory, resulting in slower moving circulation systems. More prolonged weather conditions enhance the probability for extreme weather due to drought, flooding, cold spells, and heat waves. The second effect is a northward elongation of ridge peaks in 500 hPa waves, which amplifies the flow trajectory and further exacerbates the increased probability of slow‐moving weather patterns. While Arctic amplification during autumn and winter is largely driven by sea‐ice loss and the subsequent transfer of additional energy from the ocean into the high‐latitude atmosphere, the increasing tendency for high‐amplitude patterns in summer is consistent with enhanced warming over high‐latitude land caused by earlier snow melt and drying of the soil. Enhanced 500‐hPa ridging observed over the eastern N. Atlantic is consistent with more persistent high surface pressure over western Europe. This effect has been implicated as contributing to record heat waves in Europe during recent summers.

And for the record, here are the GFS northern hemisphere 500hPa charts for the 5th, 10th and 14th of June 2019 illustrating how the pattern has not changed much over the last two weeks:

152016842_GFSNH05Jun.thumb.png.a65e6cd544f6988c7803cbc5310496fc.png 1743482069_GFSNH10Jun.thumb.png.d09193ff4eecd42f92f3d02db2d19126.png 187121396_GFSNH14Jun.thumb.png.dca85b1e24334f1e99c7c88f528360d2.png

 

Edited by Blessed Weather

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Posted (edited)

Thanks Malcom. Relevant here is this article also - can both coexist happily?

https://journals.ametsoc.org/doi/full/10.1175/JCLI-D-14-00632.1

From the summary:

"To first order, the magnitudes of the meridional potential temperature gradient and of the mixing length determine the synoptic potential temperature variance near the surface in midlatitudes. Arctic amplification of global warming leads to a reduction of the meridional potential temperature gradient that is expected to be larger than any changes in mixing length (especially in winter), leading to a reduction of the synoptic potential temperature variance near the surface."

and

"Idealized GCMs and comprehensive climate models robustly show that the synoptic potential temperature variance indeed decreases in midlatitudes of the Northern Hemisphere as the climate warms, especially in winter (when Arctic amplification is strong). Most of that variance reduction can be attributed to a reduction of the meridional potential temperature gradient, consistent with the findings of Screen (2014). But changes in the mixing length and other processes also play a role."

and

"Taken together, these findings indicate that Arctic amplification of global warming leads to even less frequent cold outbreaks in the Northern Hemispheric winter than are already implied by a shift toward a warmer mean climate. We did not examine specifically how the frequency of blocking episodes changes with climate (cf. Liu et al. 2012; Hassanzadeh et al. 2014). However, our analyses suggest they do not modify synoptic potential temperature variations and/or their departures from Gaussian statistics substantially."

 

Edited by Catacol

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On 16/06/2019 at 23:02, Catacol said:

Thanks Malcom. Relevant here is this article also - can both coexist happily?

(SNIPPED)

Many thanks for the paper Catacol - I've added it to the Research library. There does appear to be some differences between the two papers, but if I'm reading them correctly, they are in agreement about increased frequency of blocking during the summer months. I note that one paper focuses on blocking patterns in winter, where it finds no significant increase in events, and the other paper focuses on the causes of summer heatwaves, where it does find an increase.

And right on cue, with mainland Europe currently in the grip of a heatwave, Kai Kornhuber, the lead author of the paper Extreme weather events in early summer 2018 connected by a recurrent hemispheric wave-7 pattern that we are discussing, has posted this tweet:

"Wave 7 returns and so does extreme heat in Western Europe. Just as in 2003, 2006, 2015 and 2018 this recurrent jet-stream pattern will likely fuel extreme weather in other parts of the Northern Hemisphere as well."

832983278_Wave-7Amplitude22Jun2019.thumb.jpg.37f0292c4031be7b8b975a60376845de.jpg

https://twitter.com/KKornhuber/status/1142829569969479680

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