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  1. Here are the current Papers & Articles under the research topic ENSO (El Nino Southern Oscillation) which include papers on the two variants El Nino and La Nina. Click on the title of a paper you are interested in to go straight to the full paper. Papers and articles covering the basics (ideal for learning) are shown in Green. El Niño, La Niña and the Southern Oscillation (Met Office overview) A Review of ENSO Theories Are there two types of La Nina? Are Greenhouse Gases Changing ENSO Precursors in the Western North Pacific? Causes and Predictability of the Negative Indian Ocean Dipole and Its Impact on La Niña During 2016 Combined effect of the QBO and ENSO on the MJO Different ENSO teleconnections and their effects on the stratospheric polar vortex Dynamics of the ENSO teleconnection and NAO variability in the North Atlantic-European late winter Effect of AMOC collapse on ENSO in a high resolution general circulation model Effects of stratospheric variability on El Niño teleconnections El Niño and La Niña Years and Intensities - Charts from 1950 to date El Niño, La Niña, and stratospheric sudden warmings: A re-evaluation in light of the observational record El Niño/Southern Oscillation behaviour since 1871 as diagnosed in an extended multivariate ENSO index (MEI.ext) ENSO Amplitude Modulation Associated with the Mean SST Changes in the Tropical Central Pacific Induced by Atlantic Multidecadal Oscillation ENSO Atmospheric Teleconnections and Their Response to Greenhouse Gas Forcing ENSO Modulation of MJO Teleconnections to the North Atlantic and Europe Global Warming and ENSO – A “Helter-Skelter” Atmosphere Historical El Nino and La Nina Episodes - from 1950 to date Impact of El Niño–Southern Oscillation on European climate Impact of the South and North Pacific Meridional Modes on ENSO: Observational Analysis and Comparison Impacts of high-latitude volcanic eruptions on ENSO and AMOC Importance of Late Fall ENSO Teleconnection in the Euro-Atlantic Sector Increasing Frequency of Extreme El Nino Events due to Greenhouse Warming 2014 paper. Abstract: El Niño events are a prominent feature of climate variability with global climatic impacts. The 1997/98 episode, often referred to as `the climate event of the twentieth century', and the 1982/83 extreme El Niño, featured a pronounced eastward extension of the west Pacific warm pool and development of atmospheric convection, and hence a huge rainfall increase, in the usually cold and dry equatorial eastern Pacific. Such a massive reorganization of atmospheric convection, which we define as an extreme El Niño, severely disrupted global weather patterns, affecting ecosystems, agriculture, tropical cyclones, drought, bushfires, floods and other extreme weather events worldwide. Potential future changes in such extreme El Niño occurrences could have profound socio-economic consequences. Here we present climate modelling evidence for a doubling in the occurrences in the future in response to greenhouse warming. We estimate the change by aggregating results from climate models in the Coupled Model Intercomparison Project phases 3 (CMIP3; ref. ) and 5 (CMIP5; ref. ) multi-model databases, and a perturbed physics ensemble. The increased frequency arises from a projected surface warming over the eastern equatorial Pacific that occurs faster than in the surrounding ocean waters, facilitating more occurrences of atmospheric convection in the eastern equatorial region. Indian Ocean Dipole Modes Associated with Different Types of ENSO Development Leading modes of tropical Pacific subsurface ocean temperature and associations with two types of El Niño Linking Emergence of the Central Pacific El Niño to the Atlantic Multidecadal Oscillation Look South, ENSO Forecasters On the 60-month cycle of multivariate ENSO index Pacific meridional mode and El Nino Southern Oscillation Response of the Zonal Mean Atmospheric Circulation to El Niño versus Global Warming Rossby wave dynamics of the North Pacific extra-tropical response to El Nino: Importance of the basic state in coupled GCMs Seasonal predictability of winter ENSO types in operational dynamical model predictions Separating the stratospheric and tropospheric pathways of El Niño–Southern Oscillation teleconnections Stratospheric role in interdecadal changes of El Niño impacts over Europe The Defining Characteristics of ENSO Extremes and the Strong 2015/2016 El Niño The Distinct Contributions of the Seasonal Footprinting and Charged‐Discharged Mechanisms to ENSO Complexity The impact of the AMO on multidecadal ENSO variability The impact of combined ENSO and PDO on the PNA climate:a 1,000-year climate modeling study The interaction between the Western Indian Ocean and ENSO in CESM The Northern Hemisphere Extratropical Atmospheric Circulation Response to ENSO: How Well Do We Know It and How Do We Evaluate Models Accordingly? The Relationship between Northern Hemisphere Winter Blocking and Tropical Modes of Variability 2016 paper. Abstract: In the present study, the influence of some major tropical modes of variability on Northern Hemisphere regional blocking frequency variability during boreal winter is investigated. Reanalysis data and an ensemble experiment with the ECMWF model using relaxation toward the ERA-Interim data inside the tropics areused. The tropical modes under investigation are El Niño–Southern Oscillation (ENSO), the Madden–Julian oscillation (MJO), and the upper-tropospheric equatorial zonal-mean zonal wind [U1^50]E. An early (late) MJO phase refers to the part of the MJO cycle when enhanced (suppressed) precipitation occurs over the western Indian Ocean and suppressed (enhanced) precipitation occurs over the Maritime Continent and the western tropical Pacific. Over the North Pacific sector, it is found that enhanced (suppressed) high-latitude blocking occurs in association with El Niño (La Niña) events, late (early) MJO phases, and westerly (easterly)[U1^50]E. Over central to southern Europe and the east Atlantic, it is found that late MJO phases, as well as a suppressed MJO, are leading to enhanced blocking frequency. Furthermore, early (late) MJO phases arefollowed by blocking anomalies over the western North Atlantic region, similar to those associated with a positive (negative) North Atlantic Oscillation. Over northern Europe, the easterly (westerly) phase of[U1^50]Eis associated with enhanced (suppressed) blocking. These results are largely confirmed by both the reanalysis and the model experiment. The South Pacific Meridional Mode as a Thermally Driven Source of ENSO Amplitude Modulation and Uncertainty The South Pacific Meridional Mode: A Mechanism for ENSO-like Variability The Teleconnection of El Niño Southern Oscillation to the Stratosphere Timing of subsurface heat magnitude for the growth of El Niño events Triggering of El Niño onset through trade wind–induced charging of the equatorial Pacific Unusual Behavior in Atmospheric Angular Momentum during the 1965 and 1972 El Niños Westerly Wind Bursts and Their Relationship with Intraseasonal Variations and ENSO. Part I: Statistics Westerly Wind Bursts: ENSO’s Tail Rather than the Dog? Where is ENSO stress balanced?
  2. Welcome to the latest stratospheric temperature watch thread. A bit later this year with a new thread – but better late than never! It is now the 7th winter stratospheric temperature watch thread on netweather, and how much have we learnt in the past years! As ever, the first post will become both a reference thread and basic learning thread for those wanting to understand how the stratosphere may affect the winter tropospheric pattern, so forgive me for some repeat from previous years, but it is important that those new to the stratosphere have a place that they can be directed to in order to achieve a basic grasp of the subject. The stratosphere is the layer of the atmosphere situated between 10km and 50km above the earth. It is situated directly above the troposphere, the first layer of the atmosphere and the layer that is directly responsible for the weather that we receive at the surface. The boundary between the stratosphere and the troposphere is known as the tropopause. The air pressure ranges from around 100hPa at the lower levels of the stratosphere to below 1hPa at the upper levels. The middle stratosphere is often considered to be around the 10-30hPa level. Every winter the stratosphere cools down dramatically as less solar UV radiation is absorbed by the ozone content in the stratosphere. The increasing difference in the temperature between the North Pole and the latitudes further south creates a strong vortex – the wintertime stratospheric polar vortex. The colder the polar stratosphere in relation to that at mid latitudes, the stronger this vortex becomes. The stratospheric vortex has a strong relationship with the tropospheric vortex below. A strong stratospheric vortex will lead to a strong tropospheric vortex. This relationship is interdependent; conditions in the stratosphere will influence the troposphere whilst tropospheric atmospheric and wave conditions will influence the stratospheric state. At the surface the strength and position of the tropospheric vortex influences the type of weather that we are likely to experience. A strong polar vortex is more likely to herald a positive AO with the resultant jet stream track bringing warmer and wet southwesterly winds. A weaker polar vortex can contribute to a negative AO with the resultant mild wet weather tracking further south and a more blocked pattern the result. A negative AO will lead to a greater chance of colder air spreading to latitudes further south such as the UK. AO chart The stratosphere is a far more stable environment then the troposphere below it. However, the state of the stratosphere can be influenced by numerous factors – the current solar state, the Quasi Biennial Oscillation (QBO), the ozone content and distribution and transport mechanism, the snow cover and extent indices and the ENSO state to name the most significant. These factors can influence whether large tropospheric waves that can be deflected into the stratosphere can disrupt the stratospheric polar vortex to such an extent that it feeds back into the troposphere. Ozone Content in the stratosphere Ozone is important because it absorbs UV radiation in a process that warms the stratosphere. The Ozone is formed in the tropical stratosphere and transported to the polar stratosphere by a system known as the Brewer-Dobson-Circulation (the BDC). The strength of this circulation varies from year to year and can in turn be dictated by other influences. The ozone content in the polar stratosphere has been shown to be destroyed by CFC's permeating to the stratosphere from the troposphere. The overall ozone content in the polar stratosphere will help determine the underlying polar stratospheric temperature, with higher contents of ozone leading to a warmer polar stratosphere. The ozone levels can be monitored here: http://www.cpc.ncep.noaa.gov/products/stratosphere/sbuv2to/index.shtml One of the main influences on the stratospheric state is the QBO. This is a tropical stratospheric wind that descends in an easterly then westerly direction over a period of around 28 months. This can have a direct influence on the strength of the polar vortex in itself. The easterly (negative) phase is thought to contribute to a weakening of the stratospheric polar vortex, whilst a westerly (positive) phase is thought to increase the strength of the stratospheric vortex. However, in reality the exact timing and positioning of the QBO is not precise and the timing of the descending wave can be critical throughout the winter. Diagram of the descending phases of the QBO: (with thanks from http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/qbo/index.html ) The QBO has been shown to influence the strength of the BDC, depending upon what phase it is in. The tropical upward momentum of ozone is stronger in the eQBO , whereas in the wQBO ozone transport is stronger into the lower mid latitudes, so less ozone will enter the upper tropical stratosphere to be transported to the polar stratosphere as can be seen in the following diagram. http://www.atmos-chem-phys.net/13/4563/2013/acp-13-4563-2013.pdf However, the direction of the QBO when combined with the level of solar flux has also been shown to influence the BDC. When the QBO is in a west phase during solar maximum there are more warming events in the stratosphere, as there is also during an easterly phase QBO during solar minimum, so the strength of the BDC is also affected by this – also known as the Holton Tan effect . http://strat-www.met.fu-berlin.de/labitzke/moreqbo/MZ-Labitzke-et-al-2006.pdf http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50424/abstract http://onlinelibrary.wiley.com/doi/10.1002/2013JD021352/abstract The QBO is measured at 30 hPa and has entered a westerly phase for this winter. As mentioned warming events are more likely during solar maximum when in this westerly phase – with the solar flux below 110 units. Currently, we have just experienced a weak solar maximum and the solar flux heading into winter is still around this mark. This doesn’t rule out warming events, but they will not be as likely – perhaps if the solar flux surges then the chance will increase. Latest solar flux F10.7cm: http://www.swpc.noaa.gov/products/solar-cycle-progression Sudden Stratospheric Warmings: One warming event that can occur in the stratospheric winter is a Sudden Stratospheric Warming (SSW) or also known as a Major Midwinter Warming (MMW). This, as the name suggests is a rather dramatic event. Normally the polar night jet at the boundary of the polar vortex demarcates the boundary between warmer mid latitude and colder polar stratospheric air (and ozone levels) and this is very difficult to penetrate. SSWs can be caused by large-scale planetary tropospheric (Rossby) waves being deflected up into the stratosphere and towards the North Pole, often after a strong mountain torque event. These waves can introduce warmer temperatures into the polar stratosphere which can seriously disrupt the stratospheric vortex, leading to a slowing or even reversal of the vortex. Any SSW will be triggered by the preceding tropospheric pattern - in fact the preceding troposheric pattern is important in disturbing the stratospheric vortex even without creating a SSW. Consider a tropospheric pattern where the flow is very zonal - rather like the positive AO phase in the diagram above. There has to be a mechanism to achieve a more negative AO or meridional pattern from this scenario and there is but it is not straightforward. It just doesn't occur without some type of driving mechanism. Yes, we need to look at the stratosphere - but if the stratosphere is already cold and a strong polar vortex established, then we need to look back into the troposphere. In some years the stratosphere will be more receptive to tropospheric interactions than others but we will still need a kickstart from the troposphere to feedback into the stratosphere. This kickstart will often come from the tropics in the form of pulses and patterns of convection. These can help determine the position and amplitude of the long wave undulations – Rossby waves - that are formed at the barrier between the tropospheric polar and Ferrel cells. The exact positioning of the Rossby waves will be influenced by (amongst other things) the pulses of tropical convection – such as the phase of the Madden Jullian Oscillation and the background ENSO state and that is why we monitor that so closely. These waves will interact with land masses and mountain ranges which can absorb or deflect the Rossby waves disrupting the wave pattern further - and this interaction and feedback between the tropical and polar systems is the basis of how the Global Wind Oscillation influences the global patterns. If the deflection of the Rossby Wave then a wave breaking event occurs – similar to a wave breaking on a beach – except this time the break is of atmospheric air masses. Rossby wave breaks that are directed poleward can have a greater influence on the stratosphere. The Rossby wave breaks in the troposphere can be demonstrated by this diagram below – RWB diagram: https://www.jstage.jst.go.jp/article/jmsj/86/5/86_5_613/_pdf This occurs a number of times during a typical winter and is more pronounced in the Northern Hemisphere due to the greater land mass area. Most wave deflections into the stratosphere do change the stratospheric vortex flow pattern - this will be greater if the stratosphere is more receptive to these wave breaks (and if they are substantial enough, then a SSW can occur). The change in the stratospheric flow pattern can then start to feedback into the troposphere - changing the zonal flow pattern into something with more undulations and perhaps ultimately to a very meridional flow pattern especially if a SSW occurs - but not always. If the wave breaking occurs in one place then we see a wave 1 type displacement of the stratospheric vortex, and if the wave breaking occurs in two places at once then we will see a wave 2 type disturbance of the vortex which could ultimately squeeze the vortex on half and split it – and if these are strong enough then we would see a displacement SSW and split SSW respectively. The SSW is defined by a reversal of mean zonal mean winds from westerly to easterly at 60ºN and 10hPa. This definition is under review as there have been suggestions that other warmings of the stratosphere that cause severe disruption to the vortex could and should be included. http://birner.atmos.colostate.edu/papers/Butleretal_BAMS2014_submit.pdf A demonstration of the late January 2009 SSW that was witnessed in the first strat thread has been brilliantly formulated by Andrej (recretos) and can be seen below: The effects of a SSW can be transmitted into the troposphere as the downward propagation of the SSW occurs and this can have a number of consequences. There is a higher incidence of northern blocking after SSW’s but we are all aware that not every SSW leads to northern blocking. Any northern blocking can lead to cold air from the tropospheric Arctic flooding south and colder conditions to latitudes further south can ensue. There is often thought to be a time lag between a SSW and northern blocking from any downward propagation of negative mean zonal winds from the stratosphere. This has been quoted as up to 6 weeks though it can be a lot quicker if the polar vortex is ripped in two following a split SSW. A recent paper has shown how the modelling of SSW and strong vortex conditions have been modelled over a 4 week period. This has shown that there is an increase in accuracy following weak or strong vortex events – though the one area that the ECM overestimates blocking events following an SSW at week 4 is over Northwestern Eurasia. http://iopscience.iop.org/article/10.1088/1748-9326/10/10/104007 One noticeable aspect of the recent previous winters is how the stratosphere has been susceptible to wave breaking from the troposphere through the lower reaches of the polar stratosphere - not over the top as seen in the SSWs. This has led to periods of sustained tropospheric high latitude blocking and repeated lower disruption of the stratospheric polar vortex. This has coincided with a warmer stratosphere where the mean zonal winds have been reduced and has led to some of the most potent winter spells witnessed in recent years. We have also seen in recent years following Cohen's work the importance of the rate of Eurasian snow gain and coverage during October at latitudes below 60ºN. If this is above average then there is enhanced feedback from the troposphere into the stratosphere through the Rossby wave breaking pattern described above and diagrammatically below. Six stage Cohen Process: The effect of warming of the Arctic ocean leading to colder continents with anomalous wave activity penetrating the stratosphere has also been postulated http://www.tos.org/oceanography/archive/26-4_cohen.pdf Last year we saw a large snow gain but unfortunately tropospheric atmospheric patterns prevented the full potential of these being unleashed on the stratosphere – hence no SSW, but this winter could be different, but we will have to wait until the end of October. ENSO Influences One of the main influences in the global atmospheric state this winter will be the upcoming El Nino, and that is forecast to be the strongest since 1997. Studies have shown that SSW’s are more likely during strong ENSO events ( http://www.columbia.edu/~lmp/paps/butler+polvani-GRL-2011.pdf) but also that there is a particular pattern of upward propagating waves. During El Nino events wave formation is suppressed over the Indian Ocean Basin whilst it is enhanced over the Pacific Ocean http://link.springer.com/article/10.1007%2Fs00382-015-2797-5 The ENSO pathway taken may be all critical this year as can be demonstrated by this paper http://www.columbia.edu/~lmp/paps/butler+polvani+deser-ERL-2014.pdf This can lead us to suggest that a rather distinctive wave 1 pattern is likely this winter with the trigger zone likely to be over the north Pacific in the form of a quasi stationary enhanced wave 1 – a traditional Aleutian low SSW trigger pattern is suggested by Garfinkel et al ( http://www.columbia.edu/~lmp/paps/garfinkel+etal-JGR-2012.pdf ) and this should be expected at some point this winter. The reported incidence of SSW in EL Nino years is roughly around 60% - which is more than ENSO neutral years. A big question remains however, whether the ENSO wave 1 pattern will override the negative HT effect that the wQBO with the reducing solar ouput link brings. And even if it does, and we do achieve a displacement SSW, the next question is how will this affect the Atlantic sector of the Northern Hemisphere? My suspicion is that even if we do achieve a SSW this winter it will be in the second half, and also any subsequent blocking may not be quite right for the UK and, that if we were to achieve a –ve NAO, any block will be nearer Canada than Iceland, leaving the Atlantic door ajar. It is still too early this winter to be making any definitive forecasts – the next 6 weeks are very important stratospherically, determining in what vein winter will start. Already we are seeing a forecast of weak wave activity disrupting the growing vortex and it will be interesting to see if this is repeated during November. And it will be especially interesting to see what occurs in November and what is forecast for December before winter starts because typical strong El nino wQBO stratospheric composite analogues tell an opposite story. They suggest that the stratospheric vortex will be disrupted and weaker early in the winter before gaining in strength by February. December: January February The mean zonal winds are already forecast to be below average so perhaps an early disrupted vortex is more likely this year! As ever, I will supply links to various stratospheric websites were forecasts and data can be retrieved and hope for another fascinating year of monitoring the stratosphere. GFS: http://www.cpc.ncep.noaa.gov/products/stratosphere/strat_a_f/ ECM/Berlin Site: http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/index.html Netweather: http://www.netweather.tv/index.cgi?action=stratosphere;sess=75784a98eafe97c5977e66aa65ae7d28 Instant weather maps: http://www.instantweathermaps.com/GFS-php/strat.php NASA Merra site: http://acdb-ext.gsfc.nasa.gov/Data_services/met/ann_data.html Previous stratosphere monitoring threads: 2014/2015 https://forum.netweather.tv/topic/81567-stratosphere-temperature-watch-20142015/ 2013/2014 https://forum.netweather.tv/topic/78161-stratosphere-temperature-watch-20132014/ 2012/2013 https://forum.netweather.tv/topic/74587-stratosphere-temperature-watch-20122013/ 2011/2012 https://forum.netweather.tv/topic/71340-stratosphere-temperature-watch-20112012/ 2010/2012 https://forum.netweather.tv/topic/64621-stratosphere-temperature-watch/?hl=%20stratosphere%20%20temperature%20%20watch 2009/2010 https://forum.netweather.tv/topic/57364-stratosphere-temperature-watch/ 2008/2009 https://forum.netweather.tv/topic/50299-stratosphere-temperature-watch/
  3. Looks as though an el nino is very likely with the consistent negatives that we are recieving. You can keep an eye on the daily values here! http://www.longpaddock.qld.gov.au/seasonalclimateoutlook/southernoscillationindex/30daysoivalues/
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