Teleconnections - Interactions and Impact

[Interitus]

On 31/12/2019 at 15:15, Blessed Weather said:

Indian Ocean Dipole (IOD)

The IOD has continued its sharp decline during December with a latest reported value from the Australian Met (BOM) for w/e 29th December of +0.3C, bringing the index into the 'neutral' zone (-0.4 to +0.4C). Although strangely their narrative suggests a latest value of +0.6C and anticipated drop to neutral in January, contradicting their chart which clearly states +0.3C:

Source: http://www.bom.gov.au/climate/enso/indices.shtml?bookmark=iod

 

The 0.6C figure was for the most recent weekly data prior to the Dec 24th Climate Model Summary update, the 0.3C value was the latest weekly value on Dec 29th.

Interestingly, given the association of a postive IOD with Indonesian drought, severe flooding has hit the capital Jakarta - 377.4 mm was reported in 24 hours on New Year's day at Halim Perdanakusuma airport in the southeast of the city, the highest one day total on record.

[knocker]

The Pacific Decadal Oscillation less predictable under greenhouse warming

Quote

Abstract

The Pacific Decadal Oscillation (PDO) is the most prominent form of decadal variability over the North Pacific, characterized by its horseshoe-shaped sea surface temperature anomaly pattern1,2. The PDO exerts a substantial influence on marine ecosystems, fisheries and agriculture1,2,3. Through modulating global mean temperature, the phase shift of the PDO at the end of the twentieth century is suggested to be an influential factor in the recent surface warming hiatus4,5. Determining the predictability of the PDO in a warming climate is therefore of great importance6. By analysing future climate under different emission scenarios simulated by the Coupled Model Intercomparison Project phase 5 (ref. 7), we show that the prediction lead time and the associated amplitude of the PDO decrease sharply under greenhouse warming conditions. This decrease is largely attributable to a warming-induced intensification of oceanic stratification, which accelerates the propagation of Rossby waves, shortening the PDO lifespan and suppressing its amplitude by limiting its growth time. Our results suggest that greenhouse warming will make prediction of the PDO more challenging, with far-reaching ramifications.

https://www.nature.com/articles/s41558-019-0663-x?utm_source=nclimate_etoc&utm_medium=email&utm_campaign=toc_41558_10_1&utm_content=20200103&WT.ec_id=NCLIMATE-202001&sap-outbound-id=AA0953C9CAE6DF9691DBB4EA3CE9A78534D06B63&mkt-key=005056B0331B1EE88981DBEBB133AC94

[Blessed Weather]

18 hours ago, knocker said:

Observed Relationships Between Sudden Stratospheric Warmings and European Climate Extremes

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JD030480

 

1 hour ago, knocker said:

The Pacific Decadal Oscillation less predictable under greenhouse warming

https://www.nature.com/articles/s41558-019-0663-x?utm_source=nclimate_etoc&utm_medium=email&utm_campaign=toc_41558_10_1&utm_content=20200103&WT.ec_id=NCLIMATE-202001&sap-outbound-id=AA0953C9CAE6DF9691DBB4EA3CE9A78534D06B63&mkt-key=005056B0331B1EE88981DBEBB133AC94

Thanks Knocker. Two excellent new papers. I've managed to find a free-to-view copy of the PDO paper here and have put it in the Netweather Research Library. I couldn't find a free copy of the SSW/Euro Climate paper so if anyone knows if one exists please shout.

[Interitus]

Quote

Statistical Characteristics of Major Sudden Stratospheric Warming Events in CESM1-WACCM: A Comparison with the JRA55 and NCEP/NCAR Reanalyses

 

Abstract: 

Using the historical simulation from the CESM1-WACCM coupled model and based on the JRA55 and NCEP/NCAR reanalyses, the general statistical characteristics of the major sudden stratospheric warmings (SSWs) in this stratosphere-resolving model are assessed. The statistical and diagnostic results show that CESM1-WACCM can successfully reproduce the frequency of SSW events. As in the JRA55 and NCEP/NCAR reanalyses, five or six SSW events, on average, occur in a model decade. The seasonal distribution of SSWs is also well simulated with the highest frequency in January (35%). The unprecedented low SSW frequency observed in 1990s from the two reanalyses is also identified in a model decade (1930s). In addition, the overestimated duration of SSW events in the earlier WACCM version is not identified in CESM1-WACCM when compared with the two reanalyses. The model can well reproduce the downward propagation of the stratospheric anomaly signals (i.e., zonal wind, height, temperature) following SSWs. Both the modelling and observational evidences indicate that SSWs are proceeded by the positive Pacific–North America (PNA) and negative Western Pacific (WP) pattern. The negative North Atlantic Oscillation (NAO) develops throughout the SSW life cycle, which is successfully modeled. A cold Eurasian continent–warm North American continent pattern is observed before SSWs at 850 h Pa, while the two continents are anomalously cold after SSWs in both the reanalyses and the model.

Obviously a large degree of uncertainty is involved, but what may be of particular interest in this paper is the inclusion of SSW dates in reanalysis going back to 1850!

https://www.mdpi.com/2073-4433/10/9/519/htm

 

[Blessed Weather]

QBO Update 4th Jan

The December monthly mean of the zonal wind at 30mb has just released by NOAA/ESRL/PSD and is down to 1.66 (m/s -1). The average monthly drop since the descent properly kicked in last June has been 1.85, so the Nov to Dec drop of 3.41 indicates a recent acceleration in the descent.

Source: https://www.esrl.noaa.gov/psd/data/correlation/qbo.data

And with the daily Singapore readings now fluctuating very close to the pos/neg (west/east) threshold, I think it reasonable to say we will imminently be in an eQBO phase at 30mb. Here's the daily reading for 16th Dec and 3rd Jan for comparison:

Source: https://acd-ext.gsfc.nasa.gov/Data_services/met/qbo/qbo_phase_plot.png

Edited January 4, 2020 by Blessed Weather
Tidy up.

[Blessed Weather]

Solar Activity and Impacts on European/UK Weather

The potential impact of the current low solar activity on European winter weather is an area of interest on the forum at present. There are currently 13 research papers in the Solar Cycle section of the Netweather Research Library on this topic and below I’ve drawn out some findings from just a couple of them. But first of all, for those wishing to start with the basics, a couple of links to explanations from NASA:

What Is the Solar Cycle?
Do Variations in the Solar Cycle Affect Our Climate System?

The first research I’ll draw some findings from is from a 2011 paper by the UK Met Office titled Solar forcing of winter climate variability in the Northern Hemisphere.

This report uses simulations of 80 years of solar minimum and maximum conditions using the Met Office ocean-troposphere-stratosphere-mesosphere climate model (HadGEM3) to re-create the impact on surface climate of the 11-year solar cycle. Findings include:

• A decrease in temps in the upper tropical stratosphere leads to a reduction in the pole-to-equator temp gradient resulting in reduction in sub-tropical stratospheric zonal winds by up to 10 m/s and this propagates downwards and polewards and results in a weaker stratospheric polar vortex and impact on the troposhere. This process is driven by alterations to planetary wave activity (and EP flux divergence), starting in October and with maximum impact in January.
• In winter (DJF) the simulated and observed response at solar minimum shows substantial changes over the whole northern hemisphere with sea-level pressure increases at high northern latitudes and decreases at mid-latitudes in the Atlantic basin corresponding to a negative Arctic Oscillation or North Atlantic Oscillation-like pattern (AO/NAO).
• The difference in hPa between middle-latitudes and the Arctic in the Atlantic sector shows a change in the NAO of -2.4 hPa for the model, compared to an observed change of -4.6 hPa (from reanalysis):

DJF MSLP hPa impact, Model Simulations v Data Reanalysis:

• Consistent with the model surface pressure pattern, decreased westerly flow in the Atlantic sector leads to anomalously cold near-surface temperatures over north-eastern Europe and northern Asia and mild conditions further south. This is in reasonable agreement with observations.

DJF Near Surface mean temps impact, Model Simulations v Data Reanalysis:

Of importance, the authors of this paper strike a note of caution, making clear that “However, mid-latitude climate variability depends on many factors……” (e.g. other teleconnections such as ENSO and QBO).

Next a look at the 2015 paper Regional climate impacts of a possible future grand solar minimum.

This paper looks at the possible impact of a future Maunder Minimum like scenario and finds that in 2010 there was an estimated 8% chance of a maunder minimum by 2050. The paper noted that the decline in solar activity had continued and at the time of writing (2015), was faster than any other such decline in the 9,300 years covered by the cosmogenic isotope data.

• “If this recent rate of decline is added to the analysis, the 8% probability estimate is now raised to between 15 and 20%.”

However the research finds that the impact of a Grand Minimum will only have a small impact on current global warming;

• “Any reduction in global mean near-surface temperature due to a future decline in solar activity is likely to be a small fraction of projected anthropogenic warming.”
• “The relative annual global mean near-surface temperature change for the period 2050–2099 is a cooling of 0.13C …… This offsets or delays the global warming trend by ∼2 years and is small compared with the modelled global warming. This is consistent with other recently published results which indicate that any change in global mean temperature due to a future prolonged solar minimum would do little to substantially offset or delay the warming due to projected increases in long-lived greenhouse gases.

But:

•  “……variability in ultraviolet solar irradiance is linked to modulation of the Arctic and North Atlantic Oscillations, suggesting the potential for larger regional surface climate effects.”

The research found that while cooling is evident year-round, the largest anomalies are in the northern hemisphere in boreal winter (peaking in January) and spring. Modelling experiments showed a negative AO/NAO-like mean sea-level pressure pattern is seen for DJF:

Model regional climate impacts of a possible future grand solar minimum for sea-level pressure (hPa) and near-surface temperature (°C):

The report also notes that:

•  “……low solar activity does not guarantee cold conditions in any specific European winter as additional variability is introduced by other factors. The 360-year Central England Temperature record for December–February shows that the coldest winters in the UK occurred at low solar activity, but, for example, 1685/6, near the centre of the Maunder minimum, was the 5th warmest winter in the entire record. This highlights the fact that solar variability acts only to bias the intrinsic year-to-year variability, which remains substantial for this region.”

Also of note the re-analysis of the data for the 11-year solar cycle for period 1870-2010 found the impact to be significant in the Atlantic sector with the difference in hPa between middle-latitudes and the Arctic showing a reduction in the NAO of -3.2 hPa with the maximum NAO impact lagging the solar cycle minimum by ∼3–4 years.

Future Solar Activity

So where are we in the solar cycle? We are thought to be at or close to the bottom (lowest level of activity) of the current Cycle 24 and soon to move into Cycle 25.

Solar experts predict the Sun’s activity in Solar Cycle 25 is likely to be below average, similar to Solar Cycle 24. This from NOAA National Weather Service: Solar experts predict the Sun’s activity in Solar Cycle 25 to be below average, similar to Solar Cycle 24.

Conclusions

The Solar Cycle clearly influences European/UK weather via top-down stratosphere-to-troposphere impacts supportive of a negative AO/NAO, but in itself the impact is not sufficiently large to avoid being over-ridden by other teleconnections which may be forcing in a different direction.
Assuming the current Cycle 24 has indeed bottomed in 2019, the greatest impact from the current solar minimum (notwithstanding the above caveat) is likely to be felt in January 2022 and/or January 2023.

[jules216]

I haven't seen any meaningful theory that explains the quasi permanent feature of Euro high, although it has been successfully forecast for past summer and this winter, can we say it is because of colder stratosphere or IOD? Would be happy to see the research documentation to link this together, rather then just reading some suggesting posts. About time more focus is being put that way. In past lets say pre 2014, even the mild winters in UK didn't necessary mean mild winters in Europe as whole as there was more throughing activity present, though since 2013/14 we are all in it together, almost like in summer when UK taps in to continental heat more often since 2013, it is a tax we are paying for Euro high, at least in summer you can say it does reward UK but in winter it is pay back time. Our only saving comfort here in central Europe is the inversion cold that will ensure numerous ice days even without exciting synoptics, but poor poor ski resorts which will see temperatures like in April. 

[Stravaiger]

1 hour ago, jules216 said:

I haven't seen any meaningful theory that explains the quasi permanent feature of Euro high, although it has been successfully forecast for past summer and this winter, can we say it is because of colder stratosphere or IOD? Would be happy to see the research documentation to link this together, rather then just reading some suggesting posts. About time more focus is being put that way. In past lets say pre 2014, even the mild winters in UK didn't necessary mean mild winters in Europe as whole as there was more troughing activity present, though since 2013/14 we are all in it together, almost like in summer when UK taps in to continental heat more often since 2013, it is a tax we are paying for Euro high, at least in summer you can say it does reward UK but in winter it is pay back time. Our only saving comfort here in central Europe is the inversion cold that will ensure numerous ice days even without exciting synoptics, but poor poor ski resorts which will see temperatures like in April. 

I've been thinking about this too...

There is a theory (and evidence) that links anthropogenic global warming with stratospheric cooling. The latter influences the strength and speed of the tropospheric polar vortex (tPV), keeping it colder and tighter, with faster winds circulating around it (the polar night jet), which protect it from destabilising interactions with other parts of the troposphere. 

As the PV increases in strength and the boundary between polar and sub-tropical air (the polar front jet) is sucked ever further north, the sub-tropical (semi-permanent) high pressure systems ridge further north too, e.g. into Europe in winter, when normally this would be a summer phenomenon. Coupled with this is the fact that there is just less cold air to go around, due to the rapid and ongoing warming of the northern hemisphere's high latitudes, so it is no longer possible for everywhere to have an average winter, temperature wise. Somewhere will always be anomalously mild.

The bad news is that, as the greenhouse gas content of the troposphere continues to increase, less of the infra-red that Earth emits will make it to the stratosphere and warm that portion of the atmosphere. So we can expect a cold stratosphere and a tightly-wound, powerful tPV to be an even more persistent feature in the coming decades...unless something else occurs that overrides this increased GHG - stratosphere interaction

This is obviously a very simplified explanation. More info and links can be found here for those that are interested: 

Global Warming Causes Stratospheric Cooling | Weather Underground

WWW.WUNDERGROUND.COM

---

Read in-depth about causes of global warming and climate changes by top meteorologist Dr. Jeff Masters at Weather Underground.

 

[Snowy L]

25 minutes ago, Stravaiger said:

I've been thinking about this too...

There is a theory (and evidence) that links anthropogenic global warming with stratospheric cooling. The latter influences the strength and speed of the tropospheric polar vortex (tPV), keeping it colder and tighter, with faster winds circulating around it (the polar night jet), which protect it from destabilising interactions with other parts of the troposphere. 

As the PV increases in strength and the boundary between polar and sub-tropical air (the polar front jet) is sucked ever further north, the sub-tropical (semi-permanent) high pressure systems ridge further north too, e.g. into Europe in winter, when normally this would be a summer phenomenon. Coupled with this is the fact that there is just less cold air to go around, due to the rapid and ongoing warming of the northern hemisphere's high latitudes, so it is no longer possible for everywhere to have an average winter, temperature wise. Somewhere will always be anomalously mild.

The bad news is that, as the greenhouse gas content of the troposphere continues to increase, less of the infra-red that Earth emits will make it to the stratosphere and warm that portion of the atmosphere. So we can expect a cold stratosphere and a tightly-wound, powerful tPV to be an even more persistent feature in the coming decades...unless something else occurs that overrides this increased GHG - stratosphere interaction

This is obviously a very simplified explanation. More info and links can be found here for those that are interested: 

Global Warming Causes Stratospheric Cooling | Weather Underground

WWW.WUNDERGROUND.COM

---

Read in-depth about causes of global warming and climate changes by top meteorologist Dr. Jeff Masters at Weather Underground.

 

The problem with that theory is you would expect the polar regions to cool down or at least warm up at a slower rate compared to the rest of the world with all that cold air locked in there, but  pretty sure the polar regions have seen the biggest warming.

[Methuselah]

11 minutes ago, Snowy L said:

The problem with that theory is you would expect the polar regions to cool down or at least warm up at a slower rate compared to the rest of the world with all that cold air locked in there, but  pretty sure the polar regions have seen the biggest warming.

No you wouldn't SL...But you would expect the stratosphere to cool as the troposphere warms (there being only a certain amount of energy to go round, and with both energy and momentum being, at all times, fully conserved)...And, to the best of my knowledge, that is precisely what's happening...?

[Snowy L]

8 hours ago, General Cluster said:

No you wouldn't SL...But you would expect the stratosphere to cool as the troposphere warms (there being only a certain amount of energy to go round, and with both energy and momentum being, at all times, fully conserved)...And, to the best of my knowledge, that is precisely what's happening...?

I mean the stratosphere and troposphere are well-connected most of the time so if you have an incredibly strong strat-vortex with cold locked over the stratospheric North Pole you should see an incredibly strong trop-vortex with cold locked over the tropospheric North Pole therefore surface temps should be below average in the North Pole.

 

 

[Blessed Weather]

@jules216 @Stravaiger @Snowy L @General Cluster

Hi Guys. First of all just an explanation that your posts were moved here as they weren't model related and the points you were discussing are subject to multi-teleconnection influences and impacts. I'll make a quick observation to start - nearly every topic regarding weather and climate has been subject to scientific studies, so it's always worth popping into the Netweather Research Library (link at the top of every page) to see what's available, or doing your own Internet search as new research and findings are coming out all the time.

Here's my quick take on the points you were discussing, doing exactly what I recommended above. I'll sum up with a few bullets of my key findings, then list the papers and their key points.

• Persistent or stuck weather patterns - known as blocks - cause extreme weather events. Blocking patterns can be caused by multiple factors but the research shows major drivers to be SSTs, Arctic Sea Ice extent and tropical forcing particularly the MJO. The stratosphere is not an important driver (although I would argue that a SSW can cause blocking post the event).
• Scientists are not in complete agreement about the impact of global warming on future frequency of blocking, it seems the majority conclude that warming will increase instances, but at least one study says no difference and in the longer-term one study says a decrease.
• Currently, most climate forecasting models have notable weaknesses (under-estimation) in forecasting future blocking trends.

Some research papers and their findings:

Origin of variability in Northern Hemisphere winter blocking on interannual to decadal timescales (2015)

This is an excellent read. Some extracts:

• .....experiments show that realistic variability in the tropics can account for a significant part of observed interannual blocking variability but also that about half of the observed variability can only be explained by extratropical tropospheric variability. On the quasi‐decadal timescale, extratropical sea surface temperature and sea ice, in addition to tropical variability, play a more important role. The stratosphere, which has been shown to influence interannual variability of the North Atlantic Oscillation in previous studies, has no significant influence on blocking according to our analysis.
• Extratropical SST and sea ice added to realistic tropical variability enhance amplitude of ensemble mean blocking anomalies. This is consistent with the hypothesis that variability in Arctic sea ice influences blocking variability over Europe..... with particular success.
• A second candidate for the improvement in blocking variability..... is the intraseasonal Madden‐Julian Oscillation (MJO)…… a decrease in European blocking is found after MJO phases 3 and 4 that are associated with convection over the eastern Indian ocean, and an increase in blocking after MJO phases 6 and 7 that are associated with convection over the western tropical Pacific. Interestingly, an increase in European blocking can also be found after days when the MJO amplitude is lower than 0.2 (inactive MJO).

Exploring recent trends in Northern Hemisphere blocking (2014)

• Observed blocking trends are diagnosed to test the hypothesis that recent Arctic warming and sea ice loss has increased the likelihood of blocking over the Northern Hemisphere. To ensure robust results, we diagnose blocking using three unique blocking identification methods….. No clear hemispheric increase in blocking is found for any blocking index, and while seasonal increases and decreases are found for specific isolated regions and time periods, there is no instance where all three methods agree on a robust trend. Blocking is shown to exhibit large interannual and decadal variability, highlighting the difficulty in separating any potentially forced response from natural variability.

Evidence linking arctic amplification to extreme weather in Mid-Latitudes (2012)

• ……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.

Blocking and its Response to Climate Change (2018)

• There has been low confidence in predicted future changes in blocking, despite relatively good agreement between climate models on a decline in blocking. This is due to the lack of a comprehensive theory of blocking and a pervasive underestimation of blocking occurrence by models. Given the level of natural variability, it is perhaps not surprising that no fully consistent long-term trends in blocking have yet emerged in observations.

Impact of declining Arctic sea ice on winter snowfall (2012)

• While the Arctic region has been warming strongly in recent decades, anomalously large snowfall in recent winters has affected large parts of North America, Europe, and east Asia. Here we demonstrate that the decrease in autumn Arctic sea ice area is linked to changes in the winter Northern Hemisphere atmospheric circulation that have some resemblance to the negative phase of the winter Arctic oscillation. However, the atmospheric circulation change linked to the reduction of sea ice shows much broader meridional meanders in midlatitudes and clearly different interannual variability than the classical Arctic oscillation. This circulation change results in more frequent episodes of blocking patterns that lead to increased cold surges over large parts of northern continents.

Finally, the following paper (a heavy read) confirms that rising CO2 is indeed cooling the middle stratosphere. But as stated by General Cluster above, this will strengthen the SPV and if the strat couples with the troposhere this will more often than not result in a stronger Jet stream (zonal flow) and less blocking. There will be exceptions caused by other teleconnections, e.g. the current persistent Alaskan/Aleutian High pressure block is being driven by the East Pacific Oscillation (EPO) which is a persistent pressure pattern across the Pacific Ocean influenced by SSTs. Hope this all helps.

Why CO2 cools the middle atmosphere –a consolidating model perspective (2016)

 

Edited January 7, 2020 by Blessed Weather
Last para - mistakenly wrote meridional flow instead of zonal flow - now amended.

[Blessed Weather]

A few topical research papers added to the Netwx Research Library today:

Persistent shift of the Arctic polar vortex towards the Eurasian continent in recent decades (2016)
Abstract:
The wintertime Arctic stratospheric polar vortex has weakened over the past three decades, and consequently cold surface air from high latitudes is now more likely to move into the middle latitudes. However, it is not known if the location of the polar vortex has also experienced a persistent change in response to Arctic climate change and whether any changes in the vortex position have implications for the climate system. Here, through the analysis of various data sets and model simulations, we show that the Arctic polar vortex shifted persistently towards the Eurasian continent and away from North America in February over the past three decades. This shift is found to be closely related to the enhanced zonal wavenumber-1 waves in response to Arctic sea-ice loss, particularly over the Barents–Kara seas (BKS). Increased snow cover over the Eurasian continent may also have contributed to the shift. Our analysis reveals that the vortex shift induces cooling over some parts of the Eurasian continent and North America which partly offsets the tropospheric climate warming there in the past three decades. The potential vortex shift in response to persistent sea-ice loss in the future6, 7, and its associated climatic impact, deserve attention to better constrain future climate changes.

Response of the northern stratospheric polar vortex to the seasonal alignment of QBO phase transitions (2008)
Abstract:
This study considers the strength of the Northern Hemisphere Holton‐Tan effect (HTE) in terms of the phase alignment of the quasi‐biennial oscillation (QBO) with respect to the annual cycle. Using the ERA‐40 Reanalysis, it is found that the early winter (Nov–Dec) and late winter (Feb–Mar) relation between QBO phase and the strength of the stratospheric polar vortex is optimized for subsets of the 44‐year record that are chosen on the basis of the seasonality of QBO phase transitions at the 30 hPa level. The timing of phase transitions serves as a proxy for changes in the vertical structure of the QBO over the whole depth of the tropical stratosphere. The statistical significance of the Nov–Dec (Feb–Mar) HTE is greatest when 30 hPa QBO phase transitions occur 9–14 (4–9) months prior to the January of the NH winter in question. This suggests that there exists for both early and late winter a vertical structure of tropical stratospheric winds that is most effective at influencing the interannual variability of the polar vortex, and that an early (late) winter HTE is associated with an early (late) progression of QBO phase towards that structure. It is also shown that the seasonality of QBO phase transitions at 30 hPa varies on a decadal timescale, with transitions during the first half of the calendar year being relatively more common during the first half of the tropical radiosonde wind record. Combining these two results suggests that decadal changes in HTE strength could result from the changing seasonality of QBO phase transitions.

Weakening of the stratospheric polar vortex by Arctic sea-ice loss (2014)
Abstract:
Successive cold winters of severely low temperatures in recent years have had critical social and economic impacts on the mid-latitude continents in the Northern Hemisphere. Although these cold winters are thought to be partly driven by dramatic losses of Arctic sea-ice, the mechanism that links sea-ice loss to cold winters remains a subject of debate. Here, by conducting observational analyses and model experiments, we show how Arctic sea-ice loss and cold winters in extra-polar regions are dynamically connected through the polar stratosphere. We find that decreased sea-ice cover during early winter months (November-December), especially over the Barents-Kara seas, enhances the upward propagation of planetary-scale waves with wavenumbers of 1 and 2, subsequently weakening the stratospheric polar vortex in mid-winter (January-February). The weakened polar vortex preferentially induces a negative phase of Arctic Oscillation at the surface, resulting in low temperatures in mid-latitudes.

[Blessed Weather]

For the record (not literally), but the daily Arctic Oscillation (AO) index reached almost +5 sigma anomaly yesterday. The daily record of +5.9 was set on Feb 26, 1990. The daily AO index is constructed by projecting the daily (00Z) 1000mb height anomalies poleward of 20°N.

Here's the index so far this autumn/winter, showing January 2020 strongly positive so far.

Source NOAA/CPC: https://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao_index.html

For those wishing to learn more about the AO and implications of positive and negative phases, the US/National Snow and Ice Data Center provides a good explanation with illustrations: https://nsidc.org/cryosphere/icelights/2012/02/arctic-oscillation-winter-storms-and-sea-ice

But maybe a switch to negative AO on the way? The GFS Ensemble forecast holds out this possibility over the coming couple of weeks:

https://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/ao_index_ensm.shtml

 

[knocker]

A paper by Paul Roundy that may be of interest

Tropical–extratropical interactions Paul E. Roundy

http://www.atmos.albany.edu/facstaff/roundy/convection/Walich14.pdf

Edited January 15, 2020 by knocker

[Blessed Weather]

MJO Research - Update

Knocker’s paper (thank you) plus an additional 5 papers added to the Netweather Research Library MJO Section today. There are now 28 papers and articles on this topic in the library. Here are the new additions with some interesting snippets from each. Of particular interest at the moment - with the MJO entering Phase 6 on the 14th January and Phase 7 expected 19th January - are the lag timescales provided in several of the papers which I have highlighted in bold. Also of interest is the acknowledgement that the variability of the NAO is impacted by several other key teleconnections including ENSO, N. Atlantic SSTs, coupling with the stratophere and snow cover. So the big question this winter, which teleconnection(s) will have the final say on how the UK/European winter plays out?

Modulation of the Global Atmospheric Circulation by Combined Activity in the Madden–Julian Oscillation and the El Nino–Southern Oscillation during Boreal Winter (2010)

Snippets:

• A simple composite analysis demonstrates the global patterns associated with the simultaneous action of the MJO and ENSO during the Northern Hemisphere cold season. Substantial anomalies around the globe associated with such simultaneous action are not explained by simple linear combinations of composites based on the MJO and ENSO separately. These results demonstrate that when both modes are present at the same time, both need to be considered simultaneously to diagnose the associated global weather patterns.
• Variance in 300-hPa geopotential height anomalies associated with this non-linear behaviour is strongly concentrated over the North Atlantic and the Bering Sea regions.
• ……our results suggest that ENSO might substantially influence the weather over Europe by amplifying and modulating the sign of the extra-tropical response to the MJO over the North Atlantic.

MJO and its relationship to ENSO (2008)

Snippet:

• One new finding in this study is that MJO-ENSO relationship has decadal variation. The relationship between MJO in spring–summer and ENSO in autumn–winter is much more significant in the 1990s than in the 1980s. This is most probably due to the decadal variation of MJO activity and ENSO variability.

The global response to tropical heating in the Madden–Julian oscillation during the northern winter (2004)

Snippets:

• A cycle of global MJO circulation anomalies was constructed from 21 northern winter seasons of OLR and NCEP–NCAR reanalysis data.
• We are primarily concerned with the extra-tropical response to the MJO, which is much stronger in the northern hemisphere than the southern hemisphere. First, we show the correlation patterns calculated over 30◦N to 90◦N at day 19 of each integration and the time of the MJO cycle. Note that a longer time is needed (19 days) for the best extra-tropical response, compared to only 11 days for the best tropical response.
• …..a significant fraction of the observed intra-seasonal circulation could be attributed to the MJO (up to 70% for the tropical winds and 36% in the northern extra-tropics)

Predictability and Prediction of the North Atlantic Oscillation (2011)

Snippets:

• Time-lagged composites and probability analysis of the NAO index for different phases of the MJO reveal a statistically significant connection between the NAO and the tropical convection of the MJO. A significant increase of the NAO amplitude happens about 5 to 15 days after the MJO-related convection dipole anomaly develops in the tropical Indian Ocean and western Pacific region.
• On seasonal time scale, possible signal sources for NAO variability are related to processes that are external to the atmosphere. Possible processes include the forcing from the underlying sea surface temperature (SST) anomaly in the extra-tropical North Atlantic, coupling with the stratosphere, and interaction with the snow cover in Eurasia. A link between the NAO and the diabatic heating in the tropics has been suggested by several studies.

Intraseasonal interaction between the Madden–Julian Oscillation and the North Atlantic Oscillation (2008)

Snippets:

• ….the main climate intra-seasonal oscillation in the tropics—the Madden–Julian Oscillation (MJO)—controls part of the distribution and sequences of the four daily weather regimes defined over the North Atlantic–European region in winter.
• Between 1974 and 2007 the occurrence of the main 4 dominant weather patterns over the North Atlantic during boreal winter (Nov – Mar) were:
  • -NAO 20%
  • +NAO 30%
  • Atlantic Ridge 23%
  • Scandi High 27%
• Forecasts are successful in ∼70 per cent of the cases based on the knowledge of the previous ∼12-day MJO phase used as a predictor.

 

 

 

Edited January 17, 2020 by Blessed Weather

[damianslaw]

Heard alot this winter about the Indian Dipole, dictating things this year, a factor never mentioned in any other winter, why has it overidden other teleconnections this year, and why has it not been mentioned before. 

Looking ahead to next winter, two positive features for something colder will be the QBO and also coming out of solar minima.

[Blessed Weather]

2 hours ago, damianslaw said:

Heard alot this winter about the Indian Dipole, dictating things this year, a factor never mentioned in any other winter, why has it overidden other teleconnections this year, and why has it not been mentioned before. 

Looking ahead to next winter, two positive features for something colder will be the QBO and also coming out of solar minima.

This year's IOD positive phase has been the strongest for 60 years, peaking in October 2019.

And a look at the graph shows the last time the IOD peaked was Autumn 2015. And guess what followed:

The meteorology of the exceptional winter of 2015/2016 across the UK and Ireland
The meteorological winter of 2015/2016 will be remembered as another exceptional winter across the UK and Ireland, with numerous climate records broken and high impact weather events causing considerable disruption from flooding and high winds. Temperatures were also exceptionally high through much of December and in late January. In this paper we document the main meteorological and climate features that defined this exceptional winter season, and consider its wider historical context.

No wonder the Met Office forecast back in Autumn mentioned the IOD as a key influence this winter.

Finally, a very enlightened report from the BBC published back on 7th Dec 2019 - before the Australian fires - about the impact:
https://www.bbc.co.uk/news/science-environment-50602971

Edited January 17, 2020 by Blessed Weather

[damianslaw]

37 minutes ago, Blessed Weather said:

This year's IOD positive phase has been the strongest for 60 years, peaking in October 2019.

And a look at the graph shows the last time the IOD peaked was Autumn 2015. And guess what followed:

The meteorology of the exceptional winter of 2015/2016 across the UK and Ireland
The meteorological winter of 2015/2016 will be remembered as another exceptional winter across the UK and Ireland, with numerous climate records broken and high impact weather events causing considerable disruption from flooding and high winds. Temperatures were also exceptionally high through much of December and in late January. In this paper we document the main meteorological and climate features that defined this exceptional winter season, and consider its wider historical context.

No wonder the Met Office forecast back in Autumn mentioned the IOD as a key influence this winter.

Finally, a very enlightening report from the BBC published back on 7th Dec 2019 - before the Australian fires - about the impact:
https://www.bbc.co.uk/news/science-environment-50602971

So hopefully it wont be a factor next winter.. 

[Blessed Weather]

11 hours ago, damianslaw said:

So hopefully it wont be a factor next winter.. 

Hope not - a strongly positive IOD seems to be a winter killer for the UK (if cold/snow is your preference). Here's the index since 1982 showing 3 previous strong events in 1994, 1997 and 2006.

Source: https://stateoftheocean.osmc.noaa.gov/sur/ind/dmi.php

And the weather in the winters that followed?

1994/95 - Very mild with a 3-month winter average CET of 5.9C. The summer of 1995 saw a record breaking heatwave.

• A very warm 12 month period from Nov 1994 to Oct 1995. Details: https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/j.1477-8696.1997.tb06320.x

1997/98 - Very mild with a 3-month winter average CET of 6.1C. Record breaking winter warmth for the UK and Europe.

• The previous highest February (and winter) temperature observed in the United Kingdom was 67.5 degrees (19.7 Celsius) set 13 February 1998, at Royal Observatory in Greenwich, London.
• Monday's historic temperature was reached during the continuation of a major, long-lived warm spell over western Europe. Etienne Kapikian, a meteorologist for Meteo France, described the responsible air mass as "exceptionnelle" in a tweet. A massive ridge of high pressure or heat dome has sat over the region for almost a week.
• Source: https://www.sciencealert.com/this-is-fine-the-uk-just-recorded-its-hottest-winter-day-since-records-began

2006/07 - Very mild with all 3 winter months CET above long term average. This article from Philip Eden:

• Winter 2006-07 - Why so warm? https://www.weatheronline.co.uk/reports/philip-eden/Why-so-warm.htm

Source of CET readings: https://www.theweatheroutlook.com/twoother/twocontent.aspx?type=libgen&id=1499

It's too early to say what influence the IOD might have on next winter 2020/21, but the latest BOM forecast suggests will turn positive again during the coming summer.

Source: http://www.bom.gov.au/climate/enso/#tabs=Indian-Ocean

Link for winter CET values: https://www.theweatheroutlook.com/twoother/twocontent.aspx?type=libgen&id=1499

 

 

Edited January 18, 2020 by Blessed Weather
Tidied up layout

[Kirkcaldy Weather]

 

[damianslaw]

Thanks for above. It's a factor I now know about. Why is it turning positive again looking at the graph positives are followed be negatives. Surely it would be a weak positive and hopefully overridden by other factors. Interesting to compare with other peak years as you say all produced very mild winters.. the following summers were all quite different though.. but also quite extreme with heat and drought in 95 heavy rain in 98 and 07.. 

[ALL ABOARD]

Imagine how frustrating it would be that even with all our limited understanding there could be a driver out there that we have not yet discovered.

Edited January 19, 2020 by Blessed Weather
Comment edited.

[Blessed Weather]

11 hours ago, ALL ABOARD said:

Imagine how frustrating it would be that even with all our limited understanding there could be a driver out there that we have not yet discovered.

Still possible I would imagine - although I'm not sure that your suggestion of Mrs Jones hanging her smalls out in Braemar qualifies! 

The Indian Ocean Dipole wasn't 'discovered' until the 1990's by Saji et al. There are dozens of new scientific research papers published each year which are slowly increasing our understanding of the drivers and impact of various teleconnections. Probably the biggest area of better understanding yet to come will be how the various teleconnections interact and in what circumstances one (or more) will suppress or enhance another and be the dominant player; progress being made but much more needed.

This season's most notorious teleconnection seems to be the IOD, with impact across at least two continents - Europe and Australia - and arguably the globe through suppression of the MJO for a long period. 

[Kirkcaldy Weather]