long range forecasting Long range forecasting and teleconnections

[Vorticity0123]

The goal of this thread is to create a valuable learning thread about long range forecasting. First, the concept of long range forecasting will be explained in short. Thereafter, we will have a global look at the GWO (Global wind oscillation) and how it affects our weather.

 

Long range forecasting

 

Long range forecasting (10+ days out) has proven to be a very difficult subject over the past several years. It is a timeframe where global models lose their deterministic value, although they can still be used as a guide for trends. It is also a timeframe where the presence or absence of tropical convection at a given place near the equator can change the complete midlatitude synoptic setting (this is showing some resemblance to the so-called butterfly effect).

 

Fortunately, this is how far the bad news goes. Even though small details can change whole patterns, these details can be predicted to quite some extent and can even show a kind of cyclical pattern. This is, for example, the case for tropical convection activity anomalies (e.g. the MJO). That means that knowing how these patterns will develop makes one able to tell something about the weather at the midlatitudes, mainly through analogues of previous years which have seen a same kind of pattern.

 

To make this recognition of patterns somewhat easier, teleconnections have been developed. Think of the GWO (Global Wind Oscillation, a recently developed index), MJO (Madden-Julian oscillation) and ENSO (contains and explains El Nino and La Nina) to name but a few.

 

Aside from the indices listed above, a fairly new subject is stratospheric meteorology, which also has predictive value for forecasting, for example, the likehood of blocking developing at the midlatitudes. A separate thread can be found on this forum about this subject.

 

The interesting, yet complicated, part comes when one tries to interpret one teleconnection separately. This is not possible, because all the teleconnections are interrelated. For example, ENSO has an effect on the convective anomalies in the tropics (which is, in very simple terms, where the MJO relies on). Therefore, if one wants to make a very good long range forecast, all factors need to be incorporated in one view. Glacier Point, an old member of this forum, is a master on this subject.

 

For most of us, though, there is much that can still be learned about this. It would be nice to get as much input as possible on these teleconnections in order to make this a valuable thread in terms of long range forecasting all year round!

 

GWO

 

One of the several interesting teleconnections is the GWO (global wind oscillation). The part below may help in grasping the concept of this.

 

Basics of the concept

 

The GWO is an index which tells something about the amount and latitudinal localization of AAM in the atmosphere.

 

Atmospheric Angular Momentum is a conserved quantity in the atmosphere. It is defined from the Earth' axis of rotation (so from the north pole through the Earth’ core up to the South Pole). We will regard the wind speed relative to the Earth’ rotation (so the wind speed we can measure). The image below gives a good representation of how this should be visualized.

 

Visualization of AAM as it could be seen from viewing the Earth. Courtesy: COMET.

 

AAM is, in terms of the atmosphere, equal to the velocity of an air parcel times the distance it is away from the Earth’ axis. For example, at the Equator, the distance of an air parcel to the Earth’ axis is very large. Therefore, it has a relatively low velocity. When the air parcel is being carried away from the Equator, its distance relative to the Earth’ axis decreases. That means the velocity needs to increase in order to maintain conservation of AAM. As a result, the parcel will accelerate. This is all under the assumption that the parcel does not exchange AAM with the surface or other air parcels.

 

Near the equator, the wind is from west to east relative to the Earth. This, paradoxically, means the air is still moving from east to west, but at a slower speed than the Earth rotates itself. This all results in AAM being added to the atmosphere from the surface.

 

At the midlatitudes, this situation is reversed. Winds tend to flow quickly from east to west at this latitude relative to the rotation Earth. This means that the air flows from east to west even faster than the Earth rotates itself. As a result, AAM is being lost to the surface due to this imbalance.

 

The above yields a surplus of AAM at the equator and a shortage of AAM at the midlatitudes. This in turn creates a “flow†of AAM from the equator to the midlatitudes. The image above illustrates this well.

 

Mountains (courtesy to Tamara for contributing in this part)

 

Mountains can add and reduce AAM via torques (in terms of friction). This process is quite complicated, but it is an important factor for the GWO.

Basically, this event can be thought of some kind of weather event colliding with a large mountain range (Rockies, Himalaya etc.). This torque mechanism can add or remove AAM from the atmosphere.

 

Such mountain torque events can send Rossby waves into the stratosphere in a certain part of the Northern Hemisphere. The net effect of this is to create a disturbance to the polar vortex and a jet stream amplification which feeds downstream.

 

In layman’s terms a mountain torque can affect the amount of amplification that happens downstream. If, for example, the Pacific jetstream collides at the Rockies, it may via complicated mechanisms (aka the Rossby waves mentioned above) cause amplification in the flow toward Europe, causing blocking to form.

 

GWO orbit explained

 

The GWO has a cyclical nature. This means that the GWO undergoes a kind of repetitive pattern, which can be explained by a circle diagram. Analogous to the MJO, the GWO has been divided in 8 phases, each with its own characteristics. All these phases are basically a follow-up of the phase before. The GWO orbit can be best seen as a measure for the total amount of AAM in the atmosphere. Below is the GWO orbit diagram with a brief explanation of what happens at every phase.

 

Visualization of the GWO orbit

 

In phase 1, negative mountain torque removes AAM from the atmosphere. The longer the GWO stays there, the lower the amount of AAM becomes in the atmosphere. This can be thought of a Jetstream colliding at a large mountain range

 

Phase 2 and 3 generally describe low AAM values in the atmosphere (which is on average also occurring according to the conceptual model described above).

 

In phase 4 and 5, positive mountain torque adds AAM to the atmosphere. The longer the GWO remains in that position, the higher the amount of AAM becomes in the atmosphere.

 

Finally, phase 6 and 7 indicate high levels of AAM in the atmosphere.

 

Concluding remarks

 

There is much more that can be told about the GWO (and many other parameters), but that is for a later time! Any help or corrections in the explanation are greatly appreciated. Also, I hope many people will be willing to contribute to this thread! Here’s hoping that this will become a fruitful thread and a learning place for many!

 

Useful links

 

In the end, a list of links which could help for teleconnections are given here:

 

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

 

GWO composites: http://www.atmos.albany.edu/student/nschiral/comp.html

 

MJO forecasts: http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml

 

MJO composites: http://www.americanwx.com/raleighwx/MJO/MJO.html

 

Update on tropical weather (expert assessment on tropical convection, including the MJO, great link): http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ghazards/

 

ECMWF stratosphere forecast: http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/

 

Stratosphere updates: https://forum.netweather.tv/topic/81567-stratosphere-temperature-watch-20142015/

 

GWO further reading: http://www.esrl.noaa.gov/psd/map/clim/gwo.htm

 

Sources:

https://www.meted.ucar.edu/

http://www.esrl.noaa.gov/psd/map/clim/test_maproom.html

[Trom]

Good post on an area that I've been exploring myself.  

 

Regarding mountain torques I had a good exchange with Tamara on this subject - it's certainly a interesting topic.  The model thread often gets focused on the stratospheres impact on the troposphere particularly via warnings but of course it works two ways and the Rossby waves deflecting upwards are an important influence and driver of the warmings.

 

There's actually a nice wiki entry on the subject http://en.wikipedia.org/wiki/Rossby_wave

 

I still have plenty to learn on this subject but thought your post was a very tidy and clear summary.

[Interitus]

This link (posted previously in the stratosphere thread) gives a good description and practical demonstration of Rossby waves and topographic forcing (video uses QuickTime) - http://geosci.uchicago.edu/~nnn/LAB/DEMOS/RossbyWave.html

[mcweather]

Great to see this thread up and running.

 

There is much to be gleaned in terms of longer range forecasting  through the teleconnections and  atmospheric drivers that the like of Tamara, Vorticity and the much missed GP tried to interpret on our behalf.

[Vorticity0123]

Thanks for the links on Rossby waves! Understanding these waves is definitely a good step in order to get a grasp of the physical background of the various teleconnections, both explaining tropical-extratropical interactions as well as stratospheric impacts.

 

For now I will do my first teleconnective forecast in this thread, attempting to connect the teleconnections with what the models are showing. So basically it will be a complementary forecast, because teleconnections may explain why a given model solution is likely to occur or not at all.

 

First, we will take a look at the current picture (of the Northern Half), to see what kind of patterns we are able to identify beforehand.

 

Current picture

 

For showing the current picture the latest GFS analysis will be used.

 

GFS surface level pressure and 500 hPa heights, 12Z run (Analysis).

 

What can be seen is that there is a 500 hPa ridge over Europe originating from the Azores high. This pattern has occurred more this winter, most evidently during last week and the week before that.

 

Also, a repetitive pattern can be seen over the US with a West Coast ridge along with an East-US trough. This pattern has been responsible for the severe drought that has occurred over California over the last few years.

 

Model forecast for week out

 

Looking at a week from now, the pattern is forecast to shift slightly, as can be seen on the GFS and ECMWF runs for 7 days from now:

 

http://www.wetterzentrale.de/pics/Recmnh1681.gif (ECMWF)

 

http://www.wetterzentrale.de/pics/Rhavn1681.gif (GFS)

 

Both models show that the ridging toward Europe will dissipate, giving way to a more zonal flow and more low pressure activity (especially at the northern parts of the UK). However, the Azores high remains quite prominently positioned to the west of Spain (slightly west of its current position).

 

Over the US, the same pattern continues to exist, though the West Coast ridge seems to be positioned somewhat more to the west on both models and the ridge is slightly less strong on the ECMWF.

 

Teleconnections

 

MJO

 

The MJO has been rather inactive over the past few weeks. This can also be seen on the GFS ensemble forecast for the MJO:

 

GFS ensemble MJO forecast for the next two weeks. The operational forecast is in green.

 

Based on this (lack of a) signal, the MJO will not be a significant guide for the weather over the next few weeks.

 

This is confirmed by the CPC (Climate prediction center), quoting from their discussion:

 

 

During the past week, the MJO remained weak. The CPC Velocity Potential based MJO index indicates some signal over the Americas that is most likely related to Kelvin Wave activity. Globally, OLR, zonal wind anomaly, and velocity potential anomaly patterns are not consistent with MJO activity. Time-Longitude plots of OLR indicate significant influence from an Equatorial Rossby Wave (ERW) near the Maritime Continent, which appears to be the most dominant signal.

Dynamical model forecasts of the MJO indicate little to no signal through Week-2. The various models indicate little to no signal in RMM phase space, with some models strengthening the signal over the Maritime Continent and others over the Western Pacific, or not at all. Statistical models are generally unreliable when seeded with a weak initial signal. Based on the observational evidence and model output, the MJO is not forecast to contribute significantly to the pattern of tropical convection during the next two weeks.

 

Source: http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ghazards/

 

Based on this, the MJO can best not be used as a parameter in a forecast.

ENSO

 

Next, we turn our vision to ENSO (contains El Nino and La Nina).

 

We are experiencing positive SST (sea surface temperature) anomalies in the Pacific, but they are not placed at places which definitely suggest an El Nino is going on.

 

Sea surface temperature anomalies in the tropical Pacific as observed over the past few weeks.

 

There is a large swath of positive SST anomalies near California (warmer than average SSTS), but this anomaly is not directly associated to an El Nino event. What can be said, though, is that the observed anomalies are positive, which suggest that a very weak El Nino signature could be present in the ocean.

 

However, the atmosphere has been rather reluctant to responding to this so far, behaving itself more La Nina-like. This has consequences for the next teleconnection, being the GWO.

 

GWO

 

The GWO has been rather La Nina-like over the winter so far (negative AAM values), and after an inactive period the GWO is forecast to go negative again (as forecasted by successive runs of the GFS):

 

GFS GWO forecast for the next couple of days.

 

After going to phase 2 (which means the atmosphere is losing AAM via mountain torque events), the GWO enters phase 2 at quite significant amplitude.

 

According to the tutorial above, phase 2 is accompanied by northward momentum transport (possibly to balance out the shortage of AAM developed at the midlatitudes).

 

Taking a look at the anomaly composites belonging to that phase, one gets the following pattern:

 

GFS 500 hPa anomalies belonging to GWO phase 2 in February.

 

It is important to focus on the overall pattern, not the details.

 

What can be seen in the analogy is that the Azores high is on average stronger than normal (in this phase). However, it is also much further west than its usual position, being located near the east coast of the US. Also, there appears to be a strong ridge to the west of the US. Finally, deeper than average troughing appears to exist near Iceland (positive NAO signal).

 

Comparing this to the actual situation (so the situation discussed at the beginning of this post) both the Pacific ridge and the Azores high are more dominant than normal in both cases. However, on the GWO analogy both ridges are located further to the west of the current position, meaning the whole pattern would have to retrogress some (move westward) in order to match this pattern.

 

Stratosphere

 

At the time of writing, little appears to be going on in the stratosphere, with little wave activity being noted. The current structure of the stratosphere (at least at 100 hPa) matches the synoptic signature at 500 hPa reasonably well. This can be seen below:

 

100 hPa heights as analysed by the ECMWF (from yesterday).

 

A clear ridge can be identified over the West Coast of the US. Furthermore, a ridge is also visible over Europe (isolines pointing poleward).

A trough can be seen over the central and eastern parts of the US as well, along with a split vortex with one part over Greenland and another over Siberia.

 

If one looks 10 days later (so 9 days from now), the following can be seen:

 

100 hPa heights for 10 days out as forecasted by the ECMWF (from yesterday).

 

The signals for a ridge over the US, and the ridge over Europe seem to have dissipated. On the other hand, the split vortex signature is still visible. Furthermore, there is little to note except a weak troughing signal over Europe, but I do not think that signal is very significant.

 

Back to models: 8-14 500 hPa NOAA forecast

 

Usually a good signal to see whether any pattern change is on the way, regardless of connections, is the 500 hPa anomalies as assessed by NOAA. Check the image below:

 

NOAA 8-14 day 500 hPa heights (green) and anomalies (red/blue).

 

The first thing that comes to attention is that the ridge over the West Coast of the US is no longer forecast to persist. In fact, it is expected to move to the west (i.e. retrogress) toward the Pacific, which is in agreement with the GWO signal.

 

Funnily enough, NOAA has just picked up this signal, as can be read in their daily discussion:

 

 THE MAJOR PATTERN CHANGE ACROSS THE NORTH PACIFIC IS WELL  AGREED UPON AMONG THE 0Z/6Z GFS AND 0Z ECMWF WHICH NOW HAVE A LARGE POSITIVE  HEIGHT ANOMALY CENTER CLOSE TO THE DATE LINE. THE LATEST HIGH RESOLUTION 12Z  GFS ALSO SUPPORTS THESE ENSEMBLE MEANS SOLUTIONS ACROSS THE NORTH PACIFIC.  

 

Source: http://www.cpc.ncep.noaa.gov/products/predictions/610day/fxus06.html

 

The major pattern change that NOAA is advertising is the shift of the West Coast ridge toward the west over the Pacific.

 

On the other hand, the Azores ridge appears to be willing to ridge toward Europe again (isohypses pointing northeastward in Europe). This is not in agreement with the GWO signal, but it does match with what we have seen over the past few weeks.

 

Conclusion

 

At first hand, there seems to be a shift toward more zonal flow over Europe. Some teleconnections, like the MJO, have not yet been able to add anything in terms of a forecast. However, interesting signals have emerged over the Pacific with the shift of the West Coast ridge toward the Pacific, which is in agreement with GWO signals. Signals for Azores high retrogression (which could be expected via the GWO) have not yet showed up. It would be interesting to see whether models will pick up on this signal on later runs.

 

It has become a rather lengthy post for a first analysis, there is just too much that can be told and looked at . I hope this analysis will give you some idea of how the pattern will evolve. Any remarks or corrections are very welcome. Also, do not hesitate to post your own analysis!

 

Sources:

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ghazards/

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/foregfs.shtml

http://www.wetterzentrale.de/topkarten/fsecmeur.html

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/enso.shtml

https://forum.netweather.tv/topic/81567-stratosphere-temperature-watch-20142015/page-71

http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/

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

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

http://www.cpc.ncep.noaa.gov/products/predictions/610day/fxus06.html

[Winter Cold]

Great post Vorticity!

 

Im really looking forward to reading this new thread and I am going to learn much from it. Its very interesting to look at the whole picture and global drivers etc. Good stuff

 

I cant wait for more posts to come from you and Tamara etc!

[Nouska]

A question for Vorticity.....

 

Why have you used the JFM rather than the FMA composites? As said on model thread, I don't know a lot about this subject so would be interested to know if there is a lag that indicates we should be back two months for the composite rather than use middle month (March) which is the one that the current mid term forecast goes into.

 

Both those composites have a tendency to Greenland blocking - as per IF, isn't that what the GloSea5 was showing for March?

 

[Tamara]

Its worth interpreting the GWO phase composites in the same way as one might interpret agreement of the NOAA upper height anomalies and the variance in scope they still can offer for surface pressure features. As per these upper height anomaly forecasts, we should be equally careful in not taking GWO composite charts too literally at face value - but interpret them taking into account the large scale number of drivers operating at any given time within the hemisphere.

 

Activity within, and the overall state of, the stratospheric polar field also play a large part in how we interpret the GWO composites. Clearly within any amplified pattern context, the strength and orientation of the polar vortex will determine how much meridional forcing can be achieved within the boundary of the polar front jet. This especially applies to the dominant La Nina type -ve tendency AAM state that has existed throughout the winter, and looks set to continue for the foreseeable future

 

Why is this?

 

Much as regularly posted on the MOD thread, a Nina type atmospheric state in the winter season supports the development of sub tropical ridging into mid latitudes - and a prevailing +NAO. Easterly wind surges in the tropics pump up these ridges and the extra strength we have kept seeing in the Azores High has limited the extent of amplification potential along the PFJ.

 

It has only been when the stratospheric vortex was displaced our side of the pole at the turn of the month, that we have seen more sustained amplification along the PFJ. But its worth remembering that it is the same GWO cycle through -ve MT stage 8/1, which is the signal to retrogress the pattern upstream in the Pacific (withdraw the Azores ridge westwards in the Atlantic) that occurred in late January, prior to the sustained amplification into February, as we are seeing right now in the modelling. In fact the cycle was initiated in mid late December and occurred a second time in mid January before this.

 

Each time through the course of this winter has seen a different amplification strength and longevity - but the NH sequence of upstream retrogression has near enough identically been in accord with GWO winter month composites under GWO Phase 1/2 -ve AAM momentum. With the caveat that AAM showed signs of Nino breakthrough into GWO Phases 4/5 after mid Jan. This led to a +EAMT which gave some hopes towards a partial resurgence at least of the autumn Siberian High SIA/SCE -AO feedback loops which went AWOL into the start of winter

 

We saw this late January

 

http://modeles.meteociel.fr/modeles/gfs/archives/gfsnh-2015012900-0-6.png

 

Whilst the GWO orbit was headed right to where we are now. Compared to this

 

http://www.meteociel.com/modeles/ecmwf/runs/2015021812/ECH1-96.GIF?18-0

 

Overall similarities in terms of the westward retraction of the Azores High, and the more NW/SE axis of troughing in the Atlantic from the upper vortex which is the result of tanking -AAM in the atmosphere, with Pacific Rossby wave activity initiated through -ve MT occuring across the US as the GWO orbits into Phase 1

 

And we have a near replica copy of predicted GWO orbit imminently, as late January, through another fairly high amplitude orbit Phase 1/2 to reflect these synoptics

 

http://www.atmos.albany.edu/student/nschiral/research/gwo/gfsgwo_1.png

 

Look however at the quite different ways that the polar profile is modelled in each of those meteocil charts. This has implications for how the jet axis will behave in the Atlantic and impacts on our surface weather.

 

The difference this time is that we do not have that displaced vortex signal to sustain any upstream amplification signal feeding downstream as the Azores High retreats westwards. Also, we have more stubborn easterly trade winds underpinning the strength of the Azores High, and correspondingly greater westerly momentum transport at mid to higher latitudes.

 

This means that amplification along the PFJ is limited this time around and whilst we see a persistence of a NW-SE jet axis, with repeated PM incursions suggested, we do not expect to see the jet digging N-S and a pronounced amplified Atlantic ridge on a sustained basis such as we saw into early February with charts like this.

 

http://modeles.meteociel.fr/modeles/gfs/archives/gfsnh-2015020200-0-6.png

 

So, in summary, same GWO orbit cycle at very similar amplitude to previously- but different surface implications for the UK in terms of how much, and how sustained the jet amplification is that verifies.

 

Both instances however, fit perfectly within the GWO Phase 1/2 composite expectations for Jan/Feb

 

Shortening wave lengths into Spring, under the same negative tendency atmospheric patterns, start to have different implications for amplification behaviour and also surface positioning of the same Atlantic ridging profile of the winter.

 

But that is best discussed and illustrated if and when we come to it

 

Updated early March :  Phase 1/2/3 GWO orbit losing weak/moderate amplitude and heading back to no coherent phasing and little forcing on patterns. Much as was seen towards the end of the first week of February (following polar vortex displacement). This, in conjunction with continued +AO profile and MJO tropical signal supports return of mid latitude ridging as signalled by models.

 

Indicated lack of frictional and MT's highly reduce the chances of significant amplification in the meantime and will continue to support and strengthen mid latitude ridging. On this basis, expectations of the jet stream remaining to the north of these ridges in tandem with +AO mean that any attempted breakdown from the north is going to be hard to achieve into the medium term in many southern part of the UK.

 

Updated 5/3/15 : Interesting changes to the AAM budget which suggests a shift towards +ve tendency. This change quite likely ocean> atmosphere linked through the latest Kelvin wave in the Pacific and the implications for the ENSO regions in the Pacific (and the MJO).

 

The GWO is forecast to break through Phase 5 into low amplitude Phases 6 and 7. This signals a modest +EAMT, and albeit only low amplitude GWO forcing suggested at the moment, it should still be enough for some warming in the stratosphere this side of the pole as a consequence of the Asian MT wave breaking activity. In tandem with MJO phasing, it gives support for blocking towards Scandinavia which the models are picking up on.

 

The coming days may well increase this signal to a higher amplitude and further increase confidence for blocking

 

This was exactly what I was looking for a month or so back to provide a much more interesting finish to winter. 5 to 6 weeks later on, the potential for cold is clearly blunted and offset by much greater insolation. March 2013 was exceptional because the Siberian feedbacks were already evident in our weather patterns in the heart of winter - hence the very deep cold pooling which occurred.

 

http://www.atmos.albany.edu/student/nschiral/research/gwo/gfsgwo_1.png

[Ali1977]

Very good posts above, are any of you willing to make a prediction for next winter - on drivers and signs as I know models are not worth looking at.  Is America going to make it 3 in a row for exceptionally cold to the NE and are we going to have another winter with a lack of HLB or MLB....Prob way too early for this but would be nice to read your thoughts.

[Cloud 10]

Lots going on in the oscillation department at the moment!

 

The AO is tanking positive but maybe becoming to big for its boots?

 

 

 

 

The MJO (gfs) looks to have been on the Red Bull,with MOGREPS heading the same way.

 

 

 

Looks like a recipe for some major changes across the Northern Hemisphere this month.

 

 

Just to add that the GWO is going off the scale as well.

 

http://www.atmos.albany.edu/student/nschiral/research/gwo/gfsgwo_1.png

[Nouska]

I'm not sure if this is the correct area for this post as the subject is not strictly a teleconnection. The Atlantic multidecadal overturning circulation (AMOC) has been in the news recently regarding possible regional climate change with several new papers suggesting a decline over the next few decades.

 

The website of the AMOC monitoring array has some very interesting articles and also the data collection updates. This article in the publications section caught my attention and may be of value in long range forecasting. Some of the coldest winters coincide with a drop in overturning speed - big question I have - is it cause or effect?

 

http://link.springer.com/article/10.1007/s00382-014-2274-6/fulltext.html

 

 

We construct a composite of the AMOC anomalies (Ψ′) from the five eddy permitting hindcasts that span the time period 1958-2001 by removing the linear trend from each ensemble member and then removing the seasonal cycle. The AMOC anomalies are then averaged to produce the ensemble mean (Fig. 2). This composite reveals several strongly negative events, some substantially in excess of 2 standard deviations from the mean. There is a strong negative event in 1962/63, one in 1980/81 and another in 1983/84. There is also a minimum in 1986/87 with a duration of 3–4 months. We can also identify two pairs of events, one pair in 1968/69 and 1969/70, and another pair in 1977/78 and 1978/79. One further example in the time series which may also be a weaker analogue of the 2009/10 event occurs during 1996/97 and 1997/98. The event in the winter of 1996/97 occurs slightly later (around March) than other events in the time series (typically January-February). It coincides with an anomalously strong northward Ekman transport anomaly in February, which we suggest is likely to have reduced the impact and altered the timing of the negative event.

 

Full menu here  http://www.rapid.ac.uk/rapidmoc/

[Vorticity0123]

After a long period of silence, here is an update on the teleconnective field. Summer has become established across the Northern Hemisphere. Quite some things have changed in the teleconnective area, with the emergence of a full-fledged El Nino being the most important. Furthermore, we have seen a hyperactive end of June and start of July in terms of tropical cyclones, which can be nicely explained by the Madden-Julian oscillation (MJO). In this post I will explore the two aforementioned features, but I will not (yet) go over to forecasting. In short, this post is a review of a few remarkable features over the past months.

 

Significant El Nino event emerges

 

The most striking event over the past few months is the strengthening of an El Nino event. If one looks at the average sea surface temperature (SST) anomalies over the majority of June, the signature is clearly evident:

 

 

SST anomalies between June 10 and July 1 (Courtesy: NOAA).

 

Note the swath of above-average SSTS extending all the way from Peru towards the International Dateline and beyond (180 E/W). The atmosphere is responding to these anomalous SSTS by behaving as an El Nino, with more convection than average occurring in the Central Pacific near the Equator. Lots of other atmospheric occur due to this El Nino event, which can be found here: http://www.pmel.noaa.gov/tao/elnino/impacts.html#part1.

 

The atmospheric 'imprint' of the El Nino has materialized this year, unlike last winter where a La Nina atmospheric pattern coincided with a sea El Nino pattern (albeit a weak one). This difference can at least partially be attributed to the fact that current El Nino event is much more vigorous than last years' one, as discussed by Tamara in the above post.

 

Much more about the current state of the El Nino event, including forecasts, can be found in the links below:

 

http://www.elnino.noaa.gov/

 

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.html

 

http://www.pmel.noaa.gov/tao/elnino/impacts.html#part1

 

http://www.wunderground.com/news/el-nino-outlook-strong-possible-may2015

 

Hyperactive tropical cyclone activity and MJO

 

During the end of June and the start of July, we have seen a hyperactive period in terms of tropical cyclones. In fact, it has been an active first half of the year 2015 in terms of tropical cyclones in the North Pacific. Up to the end of June, 11 tropical cyclones developed in these waters. July has continued the anomalous activity, as a couple of cyclones developed in early July as well.

 

Can this activity be explained by ENSO (the current El Nino event)? The answer is only to some extent and only for the Eastern and Central Pacific. As can be seen in the SST anomalies image at the start of this post, SSTS are much above average over much over the Eastern and Central Pacific, thereby aiding in tropical cyclongenesis. But what about the West Pacific?

 

More importantly, the MJO has played a major role in the tropical activity over the past month or so. Take a look at the image below:

 

Hovmoller plot: OLR anomalies averaged between 5S and 5N across the globe. The development of a tropical cyclone is indicated by a red TC mark. Courtesy: CICS-NC

 

Negative OLR (outgoing longwave radiation) anomalies indicate more than average convection whereas positive OLR anomalies indicate less than average convection. The reasoning is that convective cloud tops are relatively cold, and therefore they emit little longwave radiation. On the other hand, under clear sky conditions, the OLR is emitted mainly by the sea and the atmosphere just above, which is comparatively much warmer. As a result, the OLR is much larger.

 

An MJO event usually shows up by negative OLR anomalies (so increased convective activity) ahead of an area of positive OLR anomalies (decreased convective activity).

 

What can be seen is at the end of June, a strong MJO event developed with its axis around 60E. This event moved slowly eastward towards the International Dateline about midway in July. Interestingly, almost all tropical cyclones that formed between Mid-June and Mid-July formed at or ahead of the axis of the MJO event, just behind the time when the convection was strongest. This relationship shows that the MJO has been a major player in tropical cyclone formation over the past month.

 

Currently, we only have two tropical cyclones left, being weakening TC Dolores in the Eastern Pacific and TD Halola (which has weakened far more than anticipated initially from typhoon strength).

 

Furthermore, a great link about the MJO containing lots of neat graphs (in Hovmoller format) can be found here:

 

http://monitor.cicsnc.org/mjo/v2/

 

Last but not least, a recent paper has advertised that for forecasting MJO events, heating near the surface may be playing a key role. More here: https://forum.netweather.tv/topic/83594-lower-level-atmospheric-heating-important-for-mjo-model-simulation/

 

Summary

 

Aside from a major El Nino event, we have had a significant MJO pulse as well, which has aided in tropical cyclone formation. Much questions are not addressed yet in this post, though. The only thing that can be safely said for now is that an El Nino event will persist in the forseeable future. But what is the effect of the highly active period in terms of tropical cyclones on our own weather? Lots of 'energy' has been pumped in the extratropics, which will undoubtedly have an impact on our weather, but in which way? Is the MJO itself going to develop and can we forecast it, probably by looking at the GWO? Very interesting to say the least, but time is running short, and my knowledge is not yet great enough to answer these questions.

 

Any contributions, or possible answers to the aforementioned questions are greatly appreciated!

 

Sources:

http://www.elnino.noaa.gov/

http://www.climate.gov/news-features/blogs/enso/july-2015-el-ni%C3%B1o-update-bruce-lee

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.html

http://www.wunderground.com/news/el-nino-outlook-strong-possible-may2015

https://noaanhc.wordpress.com/

http://blog.metoffice.gov.uk/2015/07/09/multiple-tropical-cyclones-in-the-pacific/

http://www.atmos.albany.edu/student/carl/weather/index.html

http://mikeventrice.weebly.com/cckwmjo.html

http://monitor.cicsnc.org/mjo/v2/

[Vorticity0123]

 

Winter is now well underway, though it is all feeling more like mid-Autumn. The UK has been soaked over and over again, sometimes by bands of moisture-loaded conveyor belts originating all the way from the tropics. For much of Europe, December has also been a record-shattering month. In the Netherlands, the average temperature record high was literally crushed by an astounding 2.3*C!

After this extremely warm and for the UK very wet December, hopes are up that probably the rest of the winter may deliver some  wintry weather, or at least some dry spells. Will this finally be bound to come? In this post we’ll go through a journey of teleconnections in search for signals for the weather to come in the near and far future. Off we go!

Blocked and stretched

Before diving into the teleconnections, we will first examine the broad picture on the Northern Half.

GFS analysis of 500 hPa heights (colours) and surface pressure (contours) as of 12Z 03-01

Here it is important to note that the main focus will lie at the 500 hPa heights, as these are less sensitive to surface disturbances and friction. The pattern is looking far from circular to say the least. Two strong blocking highs (indicated by the black arrows) are well visible on the scene. One is located over the western US, while the other one (also the stronger one) exists over central Siberia.

In between these ridges of high pressure, an elongated area of troughing is extending all the way from Japan down to Canada (black line and blue/purple colours). This troughing is ‘squeezed’ by these two ridges of high pressure. With some imagination one might call the area of troughing indicated by the black line as being the tropospheric polar vortex (or vortices).

The same pattern up high?

The pattern described above is also nicely represented in the lower stratosphere:

ECMWF analysis of 100 hPa heights as of 12Z 03-01

Note that the orientation of the map is slightly different from the one before! Here we also see a highly elongated polar vortex stretched from Japan to Canada (indicated by the black line). The similarity to the 500 hPa pattern is quite striking. This is also the reason why I am mentioning the term ‘tropospheric polar vortex’ above, since the locations in the mid-troposphere and the lower stratosphere nearly overlap.

With a little bit of fantasy, the same ridges of high pressure can be found in the lower stratosphere as well (compared to the 500 hPa level, referred as the mid-troposphere). However, these ridges are notably less pronounced aloft.

Still cold in the Atlantic ocean – even record cold?

Time to go into the ‘deep’. As noted in the thread about the Atlantic Ocean, the ocean has been notably colder than average during the past year or so. In fact, according to Phil Klotzbach, northern parts of the North Atlantic have seen the coldest SSTS (sea surface temperatures) on record! That is quite impressive for a warming Earth to say the least.

Sea surface temperature anomalies over the past year over the Atlantic. Courtesy to Phil Klotzbach.

Unfortunately, coupling these anomalies to air pressure anomalies is hard to say the least. This has to do with the wealth of factors that affect the weather aside from the SSTS.

Very strong anomalies aloft coupled to the ocean

Still, let’s boldly see whether there is any kind of linkage. And I can say, there is quite a strong one!

500 hPa height anomalies over the past year over the Atlantic.

Negative heights (so anomalous low pressure) has dominated during 2015 near Greenland and Iceland, while positive heights (anomalous high pressure) prevailed over the Atlantic subtropics. This is typical of a positive NAO pattern.

Is it possible to couple the record low sea surface temperatures in the North Atlantic to these strong height anomalies? Probably, but for me it would go too far to put a one to one relationship here.

Still, an explanation that is possible is that the record cold North Atlantic SSTS, coupled with the slightly warmer waters in the subtropical Atlantic, strengthened the temperature gradient between these areas in the atmosphere. This could have resulted in stronger and more frequent low pressure activity over the North Atlantic.

Currently, the same SST anomaly pattern is still there. Often SSTS do not change rapidly over time, so it is a reasonably safe assumption to say that this situation will remain the same for the coming winter.

El Nino has dominated – and will continue to dominate

About ENSO we can be very brief. A strong El Nino has developed, and this El Nino appears to continue for the rest of the winter at least.

Sea surface temperature anomalies over the last week over the Eastern Pacific.

Though El Nino does not have many direct effects to our weather, it does have predictive value when looking at other subseasonal teleconnections like the MJO. So let’s take a look at these!

MJO on the run, but does it have any predictive value?

The MJO is currently rather active and located in Phase 6 or 7. The future of the MJO seems to be very uncertain yet, with the GFS and ECMWF being at two different paths so to speak.

ECMWF (left) and GFS (right) MJO forecasts per 1 January.

So, where does this bring us? According to the GFS, the MJO will remain very active and progress from phase 7 to 8. The ECMWF is much more ‘progressive’, and takes the MJO through phase 8 and 1. It also weakens the MJO significantly.

Based on the ENSO, it is possible to make composites for each phase of the MJO based on past events. In this way it enables one to forecast future pressure patterns based on past and future MJO data. This could be quite a convenient way of forecasting.

It is important to remember that these composites do not act as a literal comparison, they cannot be taken at face value. Rather, they should be used as an indication. In the links below the 500 hPa anomaly composites for each relevant phase are given for January with an El Nino active.

Phase 7 (check with the current situation!)

Phase 8

Phase 1

Phase 2

The 500 hPa anomaly pattern of the current location of the MJO (phase 7) does by no means reflect the current pattern observed at 500 hPa (see the first image of this post as a reference). The only thing I can see which matches the current situation is the high pressure activity over Siberia. Phase 8 and 1 would indicate high pressure activity over Europe or later on, Scotland, but for now these signals are not being modelled.

GWO spiking upwards

One of the strongest signals so far is the Global Wind Oscillation. It has been showing very high angular momentum amounts during the past few weeks or so.

GFS MJO forecast per 3 January.

The GWO trend is even ‘off the charts’ (rightward) today in Phase 5. Later on, the GWO is trending towards Phase 6 and 7, and probably 8 in the end. Apparently, the AAM (atmospheric angular momentum) budget is expected to remain very high over the next few days or so.

Admittedly, I am not yet skilful enough to interpret these GWO plots and translate them into something of value to the weather over Europe. For this I would refer to Glacier Point or Tamara, who are much more knowledgeable on this subject than I am

Upper stratospheric polar vortex remaining steady?

For now, it appears that the polar vortex in the upper stratosphere is not going to give way very quickly. Therefore, it does not seem to have much influence on the weather to expect in the near- and medium term. Read more here: https://forum.netweather.tv/topic/84231-stratosphere-temperature-watch-20152016/?page=21.

Blocking over the North Pole far ahead – reflecting the MJO?

In the long term, some interesting developments appear to be going to unfold.

NOAA 8-14 day 500 hPa heights (green) and anomalies (red and blue contours).

Notice the very strong positive anomalies extending from California to the North Pole. A very strong block (denoted by the black arrow) appears to be going to set up shop there. Such a strong blockade would cause very cold air to flow out over the US in the long range. The troughing remains elongated from the right parts of the North Pole towards eastern Canada. Finally, some weak blocking can be seen over the Atlantic sector as well, but the signal appears to be weak at best.

Interestingly, this situation does show quite some similarity with phase 7 of the MJO given above, notably the blocking over western Canada and troughing to the southwest of Alaska. This would make sense if the GFS MJO forecast of a few days back would come to fruition. And in this way, the signal of Atlantic blocking is reflected in the MJO as well.

Closing the scene – mixed signals?

Now that we have seen all the confusing signals, it is good to summarize them and link them together. Here we go:

1)      The northern Atlantic Ocean continues to be cooler than average, and the subtropical Atlantic warmer than average. In 2015, this has been reflected by a strong positive NAO pattern (strong low pressure near Iceland, strong high pressure near the Azores). With the SST pattern to persist, one could argue that troughing will prevail near Iceland, giving unsettled weather as a consequence. However, this relationship does not have to be a cause-effect one.

2)      El Nino remains very active.

3)      The MJO is currently active in phase 7. While MJO composites do not seem to make much sense for the time being compared to the current pattern, they appear to be becoming more and more prevalent in the future if the MJO stays in phase 7 as the GFS forecasts. This would point to a block over the Northern Atlantic, destructively interfering with the first point.

4)      The AAM budget in the atmosphere is very high and forecast to stay high for the next few weeks.

5)      The upper stratospheric polar vortex does not show any signs of weakening rapidly as of yet.

Where does this all leave us? Based on persistence, one could argue that to some extent low pressure will continue to dominate the scene near Iceland. However, this signal is more of a background signal with little value in the short-term (as in a yearly average sub seasonal variations could still be very large).

Judging from model ensemble forecasts and the MJO, ridging above the northern Atlantic appears to be a more reasonable bet. My guess is that the Atlantic ridging scenario is the most likely outcome, though the signal is at odds with the background signal for trouhging to prevail in that region. Lso, the MJO forecast is rather uncertain as well. So all in all, the statement above is not a rock solid one to say the least. Nevertheless, it will be interesting to see whether the signals mentioned above will be reflected in a few days in the models as well!

Sources:

http://www.wetterzentrale.de/topkarten/fsavnnh.html (weather maps)

www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/ (stratospheric ECMWF weather maps)

http://www.nhc.noaa.gov/aboutsst.php (SSTS)

http://www.esrl.noaa.gov/psd/cgi-bin/data/composites/printpage.pl (Very convenient site to do own climate analysis)

http://www.atmos.albany.edu/student/nschiral/gwo.html (GWO forecasts)

http://www.americanwx.com/raleighwx/MJO/MJO.html (MJO composites)

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml (MJO forecasts)

[snowking]

I haven't had much of a chance to do this for the last couple of years but I wanted to do a very crude early look at some analogue years based upon current projections for teleconnections. The three I've looked at for now are QBO, ENSO and Solar cycle progression.

For all three there is hardly a scientific methodology behind it. For QBO I took the closest matching profiles I could at 50mb (with some attention paid to 30/70mb either side of this too) - the numbers outside of brackets are the closer years I could find, the ones in brackets possess similar-ish profiles but not quite as good as the other years. This gives us a bit more data to potentially play with though. For ENSO, pretty similar to above in terms of looking at the annual profile, but here the years in brackets are years in which we remained ENSO neutral, albeit slightly negatively, where as the years outside of brackets are winters which dipped down into weak-ish La Nina.

Finally, solar cycle progression is by far the crudest of the measures. I've taken the years in the declining phase of the solar cycle with an annual smoothed sunspot number of approximately 40-50 - really not entirely scientific but within the constraints of time it should give us some idea for now.

So here were the years I picked out for each:

QBO (Close but not exact profile matches)

1962,(1965),(1972),(1974),1976,(1979),1981,(1986),2000,2014

ENSO (remained neutral rather than weak La Nina)

1954,(1961),(1962),1967,(1978),(1981),1984,1995,(2001),(2005),2007,(2012)

Solar Cycle Stage

1952,1962,1974,1984,1994,2005

The years with at least 2 'matches' are:

1962, 1974, 1981, 2005

 

I am not going to be issuing any sort of forecast based upon this very crude measure, but hopefully it's something just to get a little bit of a conversation going as we head towards the business end of the weather year - if I can get a bit more time soon then I'll try and add in some composite plots.

 

[John Badrick]

On ‎17‎/‎09‎/‎2017 at 12:57, snowking said:

I haven't had much of a chance to do this for the last couple of years but I wanted to do a very crude early look at some analogue years based upon current projections for teleconnections. The three I've looked at for now are QBO, ENSO and Solar cycle progression.

For all three there is hardly a scientific methodology behind it. For QBO I took the closest matching profiles I could at 50mb (with some attention paid to 30/70mb either side of this too) - the numbers outside of brackets are the closer years I could find, the ones in brackets possess similar-ish profiles but not quite as good as the other years. This gives us a bit more data to potentially play with though. For ENSO, pretty similar to above in terms of looking at the annual profile, but here the years in brackets are years in which we remained ENSO neutral, albeit slightly negatively, where as the years outside of brackets are winters which dipped down into weak-ish La Nina.

Finally, solar cycle progression is by far the crudest of the measures. I've taken the years in the declining phase of the solar cycle with an annual smoothed sunspot number of approximately 40-50 - really not entirely scientific but within the constraints of time it should give us some idea for now.

So here were the years I picked out for each:

QBO (Close but not exact profile matches)

1962,(1965),(1972),(1974),1976,(1979),1981,(1986),2000,2014

ENSO (remained neutral rather than weak La Nina)

1954,(1961),(1962),1967,(1978),(1981),1984,1995,(2001),(2005),2007,(2012)

Solar Cycle Stage

1952,1962,1974,1984,1994,2005

The years with at least 2 'matches' are:

1962, 1974, 1981, 2005

 

I am not going to be issuing any sort of forecast based upon this very crude measure, but hopefully it's something just to get a little bit of a conversation going as we head towards the business end of the weather year - if I can get a bit more time soon then I'll try and add in some composite plots.

 

1962!!!! YES!!!!