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Teleconnections - Interactions and Impact


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Posted
  • Location: Lincolnshire - 15m asl
  • Weather Preferences: Frost and snow. A quiet autumn day is also good.
  • Location: Lincolnshire - 15m asl
4 hours ago, Blessed Weather said:

The latest Seasonal Model updates from ECMWF, UKMO, Meteo-France, CFS, JMA, JAMSTEC, and China BCC have completed and a useful summary can be found on the SevereWeather.EU website here.

Output from 5 of these models continues to suggest a +NAO over the Winter, but I was very interested to see that the BCC model, with possible support from JAMSTEC, are both indicating the high/low pattern will be shifted further east than the traditional set-up typical of +NAO. Also, the BCC forecast strongly suggestive of a continuation of the EPO pattern discussed in an earlier post here. I've annotated the BCC chart below:

BCC 500mb Hgt Anomaly: 1069316039_BCCSeasonalOct2019.thumb.jpg.1dcb7754eda72a72cfba94680ff548bf.jpg

JAMSTEC 2m temps forecast: 841852925_JAMSTECSeasonalOct2019.thumb.jpg.2b35a836baadd023b7b70b2fa57454c7.jpg

Overall the result for the UK seems to suggest a weaker signal for low pressure and strong westerly flow, and an increased chance of colder incursions from a northerly point as a consequence of the continued EPO signal and eastward shifted +NAO with low pressure being situated over eastern Europe.

And although the BCC is out on its own, it does have some basis for its forecast, as I discussed in an earlier post here as the current descending eQBO is possibly down to around 25hPa by now (and the Berlin strat charts available from tomorrow will give a better idea). Here's the relevant bit:

....in a June 2018 paper titled: Surface impacts of the Quasi Biennial Oscillation it was found that:

“…..in early winter (December), responses to the QBO show maximum sensitivity at ∼20 hPa, but are relatively insensitive to the QBO winds below this until late winter. The impact is that Atlantic/European response is shifted eastward compared with the normal +NAO pattern.”

Comments and other thoughts most welcomed.

Hi Malcolm - this is one of those moments when I wish we could unravel the 3 months into 1 month segments. The almost permanent North Pacific ridge is a feature we are all well used to now over recent years, but this is a surprisingly strong low pressure anomaly sitting over central/Eastern Europe. The signature of the NAO is also hard to distinguish from that chart. A 3 month Euro anomaly like that sitting alongside a modest positive anomaly over Greenland suggests to me at least one period within the 3 months of significant N/NE flow. Interesting.

Edited by Catacol
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Posted
  • Location: Camborne
  • Location: Camborne

Tropopause Folds

Tropopause fold is the extrusion of stratospheric air within an upper-tropospheric baroclinic zone which slopes downward from a normal tropopause level ( ~200--300 hPa) to the middle troposphere ( ~500--700 hPa). The tropopause fold is a mesoscale feature which forms in response to strong descent at the tropopause level. It constitutes an intense phase of upper tropospheric frontal development in which thetropopause undulation collapses. In regions of confluent flow the tropopause may be deformed such that it will form a fold (as shown in Fig. 1.9) which will decay after 1 or 2 days. During the build up phase of a fold the flow is generally conservative, whereas the decay phase is characterized through nonconservative flow, e.g., diabatic heating and turbulent mixing. It is these nonconservative processes which achieve the stratosphere-troposphere exchange.

The most vigorous tropopause folds occur during the winter and spring and are less frequent than cyclone development. They are usually observed downstream from a ridge, where there is large-scale descent in the entrance region of an upper level jet streak. Ozone-rich air originates in the lower stratosphere, west of the trough axis on the cyclonic side of the upper-level jet streak. This airstream then descends anticyclonically to the lower troposphere east of the surface high-pressure system or crosses the trough axis and ascends.

Two major types of tropopause folds are noted. One is associated with the polar front jet (PFJ), which may extend deep into the troposphere along the polar front. In some PFJ tropopause folds, significant intrusion of stratospheric air deep into the troposphere occurs. The other one is associated with the subtropical jet stream (STJ) and subtropical front, which is confined in the upper troposphere only and rarely extends downward below 500 hPa. The positions of the tropical tropopause and the polar tropopause along with the formation of subtropical jet stream over the rnidlatitude region are schematically shown in Fig. 1.10. Vertical intrusions of the dynamical tropopause into the troposphere, which are folded due to differential isentropic advection, are also known as tropopause folds.

Source: Stratosphere Troposphere Interactions K Mohanahumar

792840694_fig1.thumb.JPG.6e6c3ed572c864594ae7f2baa64e93e8.JPG262807766_fig2.thumb.JPG.54685dc5e8c3e01716764278ee6efa69.JPG

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Posted
  • Location: Camborne
  • Location: Camborne

100 Years of Progress in Understanding the Stratosphere and Mesosphere

Quote

Abstract

The stratosphere contains ~17% of Earth’s atmospheric mass, but its existence was unknown until 1902. In the following decades our knowledge grew gradually as more observations of the stratosphere were made. In 1913 the ozone layer, which protects life from harmful ultraviolet radiation, was discovered. From ozone and water vapor observations, a first basic idea of a stratospheric general circulation was put forward. Since the 1950s our knowledge of the stratosphere and mesosphere has expanded rapidly, and the importance of this region in the climate system has become clear. With more observations, several new stratospheric phenomena have been discovered: the quasi-biennial oscillation, sudden stratospheric warmings, the Southern Hemisphere ozone hole, and surface weather impacts of stratospheric variability. None of these phenomena were anticipated by theory. Advances in theory have more often than not been prompted by unexplained phenomena seen in new stratospheric observations. From the 1960s onward, the importance of dynamical processes and the coupled stratosphere–troposphere circulation was realized. Since approximately 2000, better representations of the stratosphere—and even the mesosphere—have been included in climate and weather forecasting models. We now know that in order to produce accurate seasonal weather forecasts, and to predict long-term changes in climate and the future evolution of the ozone layer, models with a well-resolved stratosphere with realistic dynamics and chemistry are necessary.

https://journals.ametsoc.org/doi/full/10.1175/AMSMONOGRAPHS-D-19-0003.1#.XcGG9amJ8oA.twitter

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Posted
  • Location: Hadleigh, Suffolk
  • Weather Preferences: An Alpine climate - snowy winters and sunny summers
  • Location: Hadleigh, Suffolk

Has anyone previously picked up on the following development? According to a tweet by the World Climate Service a couple of days ago, the hitherto good correlation between the Eurasian Snow Advance Index (SAI) and the subsequent winter's AO index that existed during the period 1999 to 2013 "disappeared" in 2014 and there has been no correlation since. To me a sudden flip like this points to another teleconnection at work here - any ideas?

This October's SAI finished a reasonable 6.8 so we now wait to see if this winter's AO will return the graph line to previous years levels of correlation.

"October snow advance over Eurasia was slightly more rapid than normal this year. According to Cohen & Jones (2011), this is an indication of negative AO (cold N-Hem mid-latitudes) this winter; but in recent years the correlation has completely disappeared."

SAI Oct 2019: 226908411_OctSAIIndex1999to2019.thumb.jpg.4aea4fe31b012e2144f14c3b797cc824.jpgCorrelation with AO: 973600994_OctSAIvDJFAOcorrelation.thumb.jpg.82104cdbfa7ccdd5e7544b2fb1f39a5c.jpg

Source: Twitter @WorldClimateSvc

 

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10 hours ago, Blessed Weather said:

Has anyone previously picked up on the following development? According to a tweet by the World Climate Service a couple of days ago, the hitherto good correlation between the Eurasian Snow Advance Index (SAI) and the subsequent winter's AO index that existed during the period 1999 to 2013 "disappeared" in 2014 and there has been no correlation since. To me a sudden flip like this points to another teleconnection at work here - any ideas?

This October's SAI finished a reasonable 6.8 so we now wait to see if this winter's AO will return the graph line to previous years levels of correlation.

"October snow advance over Eurasia was slightly more rapid than normal this year. According to Cohen & Jones (2011), this is an indication of negative AO (cold N-Hem mid-latitudes) this winter; but in recent years the correlation has completely disappeared."

SAI Oct 2019: 226908411_OctSAIIndex1999to2019.thumb.jpg.4aea4fe31b012e2144f14c3b797cc824.jpgCorrelation with AO: 973600994_OctSAIvDJFAOcorrelation.thumb.jpg.82104cdbfa7ccdd5e7544b2fb1f39a5c.jpg

Source: Twitter @WorldClimateSvc

 

Yes, posted links relating to this a few times, for example, never mind 2014, this 2013 paper from Peings et al showed that using an extended dataset, the snow cover / AO relationship is non-stationary - https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2012GL054083

Other papers from Yannick Peings examine this concept further which suggests that the snow/AO correlation may just be an artefact of other processes rather than a cause itself.

 

Edited by Interitus
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Posted
  • Location: Manchester Deansgate.
  • Weather Preferences: Heavy disruptive snowfall.
  • Location: Manchester Deansgate.
12 hours ago, Blessed Weather said:

Has anyone previously picked up on the following development? According to a tweet by the World Climate Service a couple of days ago, the hitherto good correlation between the Eurasian Snow Advance Index (SAI) and the subsequent winter's AO index that existed during the period 1999 to 2013 "disappeared" in 2014 and there has been no correlation since. To me a sudden flip like this points to another teleconnection at work here - any ideas?

This October's SAI finished a reasonable 6.8 so we now wait to see if this winter's AO will return the graph line to previous years levels of correlation.

"October snow advance over Eurasia was slightly more rapid than normal this year. According to Cohen & Jones (2011), this is an indication of negative AO (cold N-Hem mid-latitudes) this winter; but in recent years the correlation has completely disappeared."

SAI Oct 2019:  AO:

Source: Twitter @WorldClimateSvc

 

Looks to me like the time when it correlates worst is after Solar max but before solar min.

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Posted
  • Location: Hadleigh, Suffolk
  • Weather Preferences: An Alpine climate - snowy winters and sunny summers
  • Location: Hadleigh, Suffolk
On 06/11/2019 at 08:10, Interitus said:

Yes, posted links relating to this a few times, for example, never mind 2014, this 2013 paper from Peings et al showed that using an extended dataset, the snow cover / AO relationship is non-stationary - https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2012GL054083

Other papers from Yannick Peings examine this concept further which suggests that the snow/AO correlation may just be an artefact of other processes rather than a cause itself.

 

Thanks Interitus. An interesting and informative paper. If I may do a quick summary of my take:

SAI/AO mechanism:
This works through positive snow anomalies enhancing the stationary wave activity flux (the propagation of stationary Rossby waves from the surface into the lower stratosphere). This upward wave momentum weakens the stratospheric polar vortex, leading to an AO response that propagates downward in winter. However, the QBO seems to be key because (as many other studies show) WAF into the stratosphere has more impact when the QBO zonal winds are easterly.

SAI/AO relationship:
This is a central question – is the relationship a cause, effect or part of a bigger feedback loop? The above mechanism seems to suggest that the SAI/AO is at the very least part of a more complex feedback mechanism that impacts NH winter weather patterns. The not-so-clear finding is that this relationship is modulated by the QBO phase with easterly phase more supportive, and the authors also leave the door open to there being impacts from other teleconnections with this remark in the conclusions:

“…further studies will be necessary to understand the multiple drivers of the AO variability and their possible interactions better….”

23 hours ago, feb1991blizzard said:

Looks to me like the time when it correlates worst is after Solar max but before solar min.

Thanks feb. An interesting observation and not without basis in-so-much as low solar activity lowers the amount of UV light reaching the earth, resulting in very cold air forming high up in the stratosphere above the equator and this anomaly then slowly descends through the atmosphere and manifests itself over the extra-tropics as a negative AO and NAO signature. So here again is another teleconnection that impacts the stratosphere which in turn impacts the AO/NAO phase. 

Further info in this paper:

Solar forcing of winter climate variability in the Northern Hemisphere
https://www.researchgate.net/publication/241606149_Solar_forcing_of_winter_climate_variability_in_the_Northern_Hemisphere

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Posted
  • Location: Wantage, Oxon
  • Weather Preferences: Hot, cold!
  • Location: Wantage, Oxon
30 minutes ago, Blessed Weather said:

 

Thanks feb. An interesting observation and not without basis in-so-much as low solar activity lowers the amount of UV light reaching the earth, resulting in very cold air forming high up in the stratosphere above the equator and this anomaly then slowly descends through the atmosphere and manifests itself over the extra-tropics as a negative AO and NAO signature. So here again is another teleconnection that impacts the stratosphere which in turn impacts the AO/NAO phase. 

Further info in this paper:

Solar forcing of winter climate variability in the Northern Hemisphere
https://www.researchgate.net/publication/241606149_Solar_forcing_of_winter_climate_variability_in_the_Northern_Hemisphere

Interesting, I'll read that.  I was struck by the following in the abstract:

"Specifically, weaker westerly winds have been observed in winters with a less active sun, for example at the minimum phase of the 11-year sunspot cycle. With some possible exceptions, it has proved difficult for climate models to consistently reproduce this signal."

If, and it is a big if, the seasonal models are missing something this year, a possible candidate there?

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Posted
  • Location: Camborne
  • Location: Camborne

Dynamics of the ENSO teleconnection and NAO variability in the North Atlantic-European late winter

Quote

Abstract

The winter extratropical teleconnection of El Niño-Southern Oscillation (ENSO) in the North Atlantic-European (NAE) sector remains controversial, concerning both the amplitude of its impacts and the underlying dynamics. However, a well-established response is a late-winter (January-March) signal in sea-level pressure (SLP) consisting of a dipolar pattern that resembles the North Atlantic Oscillation (NAO). Clarifying the relationship between this “NAOlike” ENSO signal and the actual NAO is the focus of this study. The ENSO-NAE teleconnection and NAO signature are diagnosed by means of linear regression onto the sea-surface temperature (SST) Niño3.4 index and an EOF-based NAO index, respectively, using long-term reanalysis data (NOAA-20CR, ERA-20CR). While the similarity in SLP is evident, the analysis of anomalous upper-tropospheric geopotential height, zonal wind, transient-eddy momentum flux, as well as precipitation and meridional eddy heat flux, suggests that there is no dynamical link between the phenomena. The observational results are further confirmed by analyzing two 10-member ensembles of atmosphere-only simulations (using an intermediate-complexity and a state-of-the-art model) with prescribed SSTs over the 20th century. The SSTforced variability in the Northern Hemisphere is dominated by the extratropical ENSO teleconnection, which provides modest but significant SLP skill in the NAE midlatitudes. The regional internally-generated variability, estimated from residuals around the ensemblemean, corresponds to the NAO pattern. It is concluded that distinct dynamics are at play in the ENSO-NAE teleconnection and NAO variability, and caution is advised when interpreting the former in terms of the latter.

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-19-0192.1?af=R#.XcX0P-w2iIQ.twitter

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3 hours ago, knocker said:

Dynamics of the ENSO teleconnection and NAO variability in the North Atlantic-European late winter

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-19-0192.1?af=R#.XcX0P-w2iIQ.twitter

Confirms the tenuous link between ENSO and NAO which can be gleaned from elementary investigation. Compare with this other recent paper -

The Linear Sensitivity of the North Atlantic Oscillation and Eddy-Driven Jet to SSTs

Quote

Abstract

The North Atlantic Oscillation (NAO) and eddy-driven jet contain a forced component arising from sea surface temperature (SST) variations. Due to large amounts of internal variability, it is not trivial to determine where and to what extent SSTs force the NAO and jet. A linear statistical–dynamic method is employed with a large climate ensemble to compute the sensitivities of the winter and summer NAO and jet speed and latitude to the SSTs. Key regions of sensitivity are identified in the Indian and Pacific basins, and the North Atlantic tripole. Using the sensitivity maps and a long observational SST dataset, skillful reconstructions of the NAO and jet time series are made. The ability to skillfully forecast both the winter and summer NAO using only SST anomalies is also demonstrated. The linear approach used here allows precise attribution of model forecast signals to SSTs in particular regions. Skill comes from the Atlantic and Pacific basins on short lead times, while the Indian Ocean SSTs may contribute to the longer-term NAO trend. However, despite the region of high sensitivity in the Indian Ocean, SSTs here do not provide significant skill on interannual time scales, which highlights the limitations of the imposed SST approach. Given the impact of the NAO and jet on Northern Hemisphere weather and climate, these results provide useful information that could be used for improved attribution and forecasting.

https://journals.ametsoc.org/doi/full/10.1175/JCLI-D-19-0038.1

As shown below (and with particular regard to winter) the ENSO region appears to affect NAO as part of a tropic/sub-tropic Pacific dipole. The Atlantic tripole is also in evidence, but interestingly seems to exert little more influence, though it captures most variance in reconstructed NAO time-series. However, the modeling confirms previous works, that in theory NAO is most sensitive to Indian Ocean SSTs but the influence cannot be detected interannually (eg. month to month). Rather a long term warming trend may foster periods of more positive NAO years. It is seen that prescribed Indian Ocean temperatures can be responsible for Pacific and Atlantic wave trains affecting the NAO but in reality the SSTs in the region are most sensitive to ENSO with warming forced by the atmosphere instead of SSTs forcing and preventing the teleconnection.

jcli-d-19-0038.1-f1.thumb.gif.e93a14fce01293cf3fa9ba747d9baa6b.gif

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Posted
  • Location: Hadleigh, Suffolk
  • Weather Preferences: An Alpine climate - snowy winters and sunny summers
  • Location: Hadleigh, Suffolk

Thanks Knocker. The Zonal Mean Zonal Wind charts from Berlin also provide a useful visual of how the QBO is progressing, as well as how the Stratospheric Polar Vortex is doing. Here's the ZMZW charts for 1st Nov and yesterday's forecast for the 23rd Nov, annotated to show the eQBO winds (blue) descending to almost 30hPa and the SPV westerly wind speed (red) as measured at 10hPa 60N.

1st Nov 1071365675_ECMZMZW01Nov2019.thumb.gif.e51cb2b0e7fa4ab3426a8652586ff170.gif Zoom on eQBO 942141017_ECMZMZW01Nov2019Zoom.thumb.gif.a14c277d321a2750652a3fb5c723578c.gif

23rd Nov 1784994250_ECMZMZW13Novfor23Nov2019.thumb.gif.ab0db8ff9056a3170a65d1dd1b073983.gif Zoom on eQBO 1998301853_ECMZMZW13Novfor23Nov2019Zoom.thumb.jpg.7e58653f9df933f9c9966254972cb0c9.jpg

Source: https://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/index.html

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Posted
  • Location: Hadleigh, Suffolk
  • Weather Preferences: An Alpine climate - snowy winters and sunny summers
  • Location: Hadleigh, Suffolk

The Indian Ocean Dipole (IOD)

With the IOD being mentioned in the Met Office Contingency Planners forecast and subject to discussions in other threads on here, in this post I’ll look at the basics of the IOD and how it is formed and then how, via interaction with other teleconnections, there is an impact on weather in other Regions of the World.

First the basics on the IOD. Here are two diagrams that illustrate the negative and positive phases of the IOD:

1572370470_IODnegativediag.thumb.jpg.d30d0985de627e19533ad6f59a1c32ce.jpg1530801270_IODPositiveDiag.thumb.jpg.8ab5a2f6b5ff7d9cac6618bf570052fc.jpg
Source: http://www.bom.gov.au/climate/iod/

This BOM graph shows the current strongly positive phase of the IOD up to 10th Nov:

2104666109_BOMIODWeeklyIndexto10Nov2019.thumb.png.29b4f56867ff17e987e73b25656f69cf.png
Source: http://www.bom.gov.au/climate/enso/indices.shtml?bookmark=iod

The NOAA State of the Ocean website shows the longer-term phases from the 1980’s to date and shows this year’s event only one of a handful of very strong positive phases in the last 30 years.

1302660154_IODIndexNOAA1980s-date.thumb.gif.7d091a755eed78f3d5e5944d0f5a0cf8.gif

The NOAA website also allows you to look at the component parts of the IOD – the east and west areas of the Indian Ocean - separately:

IO Index East: 1061698092_TIOSEIndexOOPsOct2019.thumb.gif.ad526b444c500838e0d044c450ffa852.gifCHART West: 1779947018_TIOWestIndexOct2019.thumb.gif.12c19c30652789d5b20ea968eee8eee7.gif
Source: https://stateoftheocean.osmc.noaa.gov/sur/ind/wtio.php  

 

So how is the IOD formed?

 First of all it should be noted that there are two different patterns of variability in the IO. The most dominant pattern is a basin wide warming of SSTs and this has a strong correlation (~0.85) with the Nino-3 index, with the latter leading the former by 4 to 6 months.

The second pattern, the IOD, can be excited by ENSO, but can also develop independently of ENSO as a seasonal event driven by ocean-atmosphere coupling in the IO itself.

“The spatio-temporal links between SST and winds reveal a strong coupling through the precipitation field and ocean dynamics. This air-sea interaction process is unique and inherent in the Indian Ocean, and is shown to be independent of the El Nino/Southern Oscillation.”
Source: A dipole mode in the tropical Indian Ocean

And extracts from the paper Ocean Circulation and Climate by Swadhin Behera in 2013:

"The stronger than normal seasonal south easterly winds along the Sumatra coast during positive IOD events cause SST cooling by coastal upwelling. Equatorial winds reverse direction from westerlies to easterlies during the peak phase of the positive IOD events and establish the characteristic dipole in the SST anomalies. The dipole in SST anomalies is accompanied by abundant rainfall over the western Indian Ocean–East Africa and scarce rainfall over eastern Indian Ocean–Indonesia. This is similar to the Bjerknes-type of air–sea interaction in the tropical Pacific. The associated mechanism is related to the propagation of oceanic Rossby–Kelvin waves where wind-stress curl associated with the IOD forces the westward propagating downwelling long Rossby waves north of 10°S."

Note that typically the IOD forms in spring, matures late summer and rapidly fades during Dec/Jan.

And what are the impacts of the IOD?

The paper The Linear Sensitivity of the North Atlantic Oscillation and Eddy-Driven Jet to SSTs introduced by Interitus a few posts back states:

“….the Indian Ocean sensitivity appears to arise from, in winter at least, the forcing of Rossby waves that constructively interfere with the climatological stationary wave, thus forcing a positive NAO response.”

The paper North Atlantic Oscillation Response to Anomalous Indian Ocean SST in a Coupled GCM finds that:

“A warming/cooling in the Indian Ocean, especially in the western Indian Ocean, produces anomalies in the South Asian jet. The wave-guiding effect of the South Asian jet carries the perturbation into the North Atlantic sector and leads to a NAO-like response.”

And the paper The Role of Linear Interference in the Annular Mode Response to Tropical SST Forcing finds:

“The tropical IO wave response attenuates the climatological wave and therefore strengthens the stratospheric jet and leads to a positive NAM response.”
…..the primary IO wave train propagates directly poleward.
…..per unit SST warming, the IO forcing is more than twice as efficient as the Pacific Ocean forcing at driving zonal mean changes at high latitudes. [Note: mentions the role of the nearby Tibetan Plateau].
…..[regarding] the EP flux and zonal wind response…. IO shows a strong westerly response in the extratropical zonal winds of the troposphere and stratosphere. For the wave activity flux into the stratosphere, the IO shows a relatively large decrease in the flux."

With apologies as this makes this post rather long, but I think it’s worth reproducing the entire Teleconnections Mechanisms section of the following paper as it is an excellent expansion of the processes involved in globally dissipating the impacts of the 1994 strong +IOD. Note that during this event the ENSO-3 index was neutral, as is the case in 2019.

The role of the Indian Ocean in climate forecasting with a particular emphasis on summer conditions in East Asia

"Teleconnections Mechanisms: The precipitation over India and the southern part of China is enhanced during the positive IOD event. The northward branch of the meridional circulation excited by the eastern pole of the positive IOD leads to the anomalous updraft and the associated divergent flow in the upper troposphere over the Tibetan Plateau. Using a simple model, we observe the anticyclonic circulation at 150 hPa west of the vorticity source region, i.e., the Tibetan Plateau. A cyclonic circulation is simultaneously generated east of the vorticity source region. A Rossby wave train is also excited, propagating northeastward from the monsoon region. The IOD-induced divergent flow in the upper troposphere near India also progresses westward and converges over Mediterranean/Sahara region. The zonal section averaged between 25°N and 35°N at 150 hPa captures the vertical circulation; the anomalous convection over India, which is induced by the IOD SSTA as explained, is amazingly linked to the anomalous decent in the Mediterranean/Sahara region.

The IOD-induced dynamic warming due to the decent of the air over the Mediterranean Sea/Sahara region and its vicinity must steadily perturb the mid-latitude westerly. Since the mid-latitude westerly acts as a Rossby wave-guide, the wave energy could propagate along the westerly, eastward to East Asia, resulting in the summer circulation variations around East Asia and the Western Pacific.

This scenario can be examined by calculating the wave activity flux (WAF). This clearly shows that the wave activity flux at 200hPa are much larger along the Asian westerly jet than those over other regions. The longitude-height cross-section shows that the anomalous wave energy propagates upward into the upper troposphere around the regions of the Mediterranean Sea, the Caspian Sea, and the East Asia along the westerly jet stream. The upward propagating wave energy in the eastern flank of the Tibetan Plateau suggests that orographic forcing also plays an important role in 1994."

With the IOD being a seasonal event peaking in late summer/Autumn, I’ll end this post with a composite of the 500mb geopotential height anomaly for the months of Jan and Feb in the winter following a positive IOD year. The Atlantic profile in the composite is a close match to and thus supports the recent Glosea5 Seasonal Forecast, although of note (and I don't have an explanation) the composite gives a strong Aleutian Low rather than Aleutian High (EPO) pattern suggested by Glosea5.

First, here are the negative and positive IOD years since records began:

1823475150_BOMIODPos-NegYears.thumb.jpg.42a68786a608acbaaadfbf3c23fa1342.jpg
Source: http://www.bom.gov.au/climate/iod/

 

Composite chart: 2045977147_IODCompositeJFyearfollowingpositive.thumb.png.698e553df5e0b2411cce3e9347f9dbb7.pngGlosea5 seasonal forecast: 11526688_Glosea5SeasonalNovforDJF2019-20.thumb.jpg.9233cb7dc854cda3f94913d4020a74fd.jpg

Source: https://www.esrl.noaa.gov/psd/cgi-bin/data/composites/printpage.pl

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6 hours ago, Blessed Weather said:

BOM graph shows the current strongly positive phase of the IOD up to 10th Nov:

 

First, here are the negative and positive IOD years since records began:

1823475150_BOMIODPos-NegYears.thumb.jpg.42a68786a608acbaaadfbf3c23fa1342.jpg
Source: http://www.bom.gov.au/climate/iod/

 

Just for fun, a quick look at CET for the +/- IOD years and other years since 1960 -

Negative years - Dec 3.94, Jan 4.46, Feb 5.42, Winter 4.61

Neutral years - Dec 4.86, Jan 3.95, Feb 3.89, Winter 4.23

Positive years - Dec 5.38, Jan 4.86, Feb 4.59, Winter 4.94

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Posted
  • Location: Camborne
  • Location: Camborne

H/t Anthony Masiello

Here's a recent paper on the climatology of Rossby Wave Breaking (Bowley et al. 2018). That area near Greenland has been very active this autumn.

https://journals.ametsoc.org/doi/pdf/10.1175/MWR-D-18-0131.1

 

Edited by knocker
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Posted
  • Location: Camborne
  • Location: Camborne

In connection with a simultaneous post of a tweet by Anthony Massiello

The North Pacific Oscillation–West Pacific Teleconnection Pattern: Mature-Phase Structure and Winter Impacts

Quote

Abstract

The North Pacific Oscillation (NPO) in sea level pressure and its upper-air geopotential height signature, the west Pacific (WP) teleconnection pattern, constitute a prominent mode of winter midlatitude variability, the NPO/WP. Its mature-phase expression is identified from principal component analysis of monthly sea level pressure variability as the second leading mode just behind the Pacific–North American variability pattern.

NPO/WP variability, primarily on subseasonal time scales, is characterized by a large-scale meridional dipole in SLP and geopotential height over the Pacific and is linked to meridional movements of the Asian–Pacific jet and Pacific storm track modulation. The hemispheric height anomalies at upper levels resemble the climatological stationary wave pattern attributed to transient eddy forcing. The NPO/WP divergent circulation is thermal wind restoring, pointing to independent forcing of jet fluctuations.

Intercomparison of sea level pressure, geopotential height, and zonal wind anomaly structure reveals that NPO/WP is a basin analog of the NAO, which is not surprising given strong links to storm track variability in both cases.

The NPO/WP variability is influential: its impact on Alaskan, Pacific Northwest, Canadian, and U.S. winter surface air temperatures is substantial—more than that of PNA or ENSO. It is likewise more influential on the Pacific Northwest, western Mexico, and south-central Great Plains winter precipitation.

Finally, and perhaps, most importantly, NPO/WP is strongly linked to marginal ice zone variability of the Arctic seas with an influence that surpasses that of other Pacific modes. Although NPO/WP variability and impacts have not been as extensively analyzed as its Pacific cousins (PNA, ENSO), it is shown to be more consequential for Arctic sea ice and North American winter hydroclimate.

https://journals.ametsoc.org/doi/full/10.1175/2007JCLI2048.1

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  • Location: Kirkcaldy, Fife, Scotland 20m ASL
  • Weather Preferences: Snow,Thunderstorms mix both for heaven THUNDERSNOW 😜😀🤤🥰
  • Location: Kirkcaldy, Fife, Scotland 20m ASL

 

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  • Location: Hadleigh, Suffolk
  • Weather Preferences: An Alpine climate - snowy winters and sunny summers
  • Location: Hadleigh, Suffolk

^ Thanks for the papers you've mentoned @knocker @Interitus and @Kirkcaldy Weather. I've added them to the Netweather Research Library. Do you guys (and anyone else) think it would be useful if I also copied the abstracts into the Library (under each paper title) so people can better see what the research covers?

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  • Location: Camborne
  • Location: Camborne
8 hours ago, Blessed Weather said:

^ Thanks for the papers you've mentoned @knocker @Interitus and @Kirkcaldy Weather. I've added them to the Netweather Research Library. Do you guys (and anyone else) think it would be useful if I also copied the abstracts into the Library (under each paper title) so people can better see what the research covers?

Yes it would be useful BW

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