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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. The goal of this thread is to create a valuable learning thread about long range forecasting. First, the concept of long range forecasting will be explained in short. Thereafter, we will have a global look at the GWO (Global wind oscillation) and how it affects our weather. Long range forecasting Long range forecasting (10+ days out) has proven to be a very difficult subject over the past several years. It is a timeframe where global models lose their deterministic value, although they can still be used as a guide for trends. It is also a timeframe where the presence or absence of tropical convection at a given place near the equator can change the complete midlatitude synoptic setting (this is showing some resemblance to the so-called butterfly effect). Fortunately, this is how far the bad news goes. Even though small details can change whole patterns, these details can be predicted to quite some extent and can even show a kind of cyclical pattern. This is, for example, the case for tropical convection activity anomalies (e.g. the MJO). That means that knowing how these patterns will develop makes one able to tell something about the weather at the midlatitudes, mainly through analogues of previous years which have seen a same kind of pattern. To make this recognition of patterns somewhat easier, teleconnections have been developed. Think of the GWO (Global Wind Oscillation, a recently developed index), MJO (Madden-Julian oscillation) and ENSO (contains and explains El Nino and La Nina) to name but a few. Aside from the indices listed above, a fairly new subject is stratospheric meteorology, which also has predictive value for forecasting, for example, the likehood of blocking developing at the midlatitudes. A separate thread can be found on this forum about this subject. The interesting, yet complicated, part comes when one tries to interpret one teleconnection separately. This is not possible, because all the teleconnections are interrelated. For example, ENSO has an effect on the convective anomalies in the tropics (which is, in very simple terms, where the MJO relies on). Therefore, if one wants to make a very good long range forecast, all factors need to be incorporated in one view. Glacier Point, an old member of this forum, is a master on this subject. For most of us, though, there is much that can still be learned about this. It would be nice to get as much input as possible on these teleconnections in order to make this a valuable thread in terms of long range forecasting all year round! GWO One of the several interesting teleconnections is the GWO (global wind oscillation). The part below may help in grasping the concept of this. Basics of the concept The GWO is an index which tells something about the amount and latitudinal localization of AAM in the atmosphere. Atmospheric Angular Momentum is a conserved quantity in the atmosphere. It is defined from the Earth' axis of rotation (so from the north pole through the Earth’ core up to the South Pole). We will regard the wind speed relative to the Earth’ rotation (so the wind speed we can measure). The image below gives a good representation of how this should be visualized. Visualization of AAM as it could be seen from viewing the Earth. Courtesy: COMET. AAM is, in terms of the atmosphere, equal to the velocity of an air parcel times the distance it is away from the Earth’ axis. For example, at the Equator, the distance of an air parcel to the Earth’ axis is very large. Therefore, it has a relatively low velocity. When the air parcel is being carried away from the Equator, its distance relative to the Earth’ axis decreases. That means the velocity needs to increase in order to maintain conservation of AAM. As a result, the parcel will accelerate. This is all under the assumption that the parcel does not exchange AAM with the surface or other air parcels. Near the equator, the wind is from west to east relative to the Earth. This, paradoxically, means the air is still moving from east to west, but at a slower speed than the Earth rotates itself. This all results in AAM being added to the atmosphere from the surface. At the midlatitudes, this situation is reversed. Winds tend to flow quickly from east to west at this latitude relative to the rotation Earth. This means that the air flows from east to west even faster than the Earth rotates itself. As a result, AAM is being lost to the surface due to this imbalance. The above yields a surplus of AAM at the equator and a shortage of AAM at the midlatitudes. This in turn creates a “flow†of AAM from the equator to the midlatitudes. The image above illustrates this well. Mountains (courtesy to Tamara for contributing in this part) Mountains can add and reduce AAM via torques (in terms of friction). This process is quite complicated, but it is an important factor for the GWO. Basically, this event can be thought of some kind of weather event colliding with a large mountain range (Rockies, Himalaya etc.). This torque mechanism can add or remove AAM from the atmosphere. Such mountain torque events can send Rossby waves into the stratosphere in a certain part of the Northern Hemisphere. The net effect of this is to create a disturbance to the polar vortex and a jet stream amplification which feeds downstream. In layman’s terms a mountain torque can affect the amount of amplification that happens downstream. If, for example, the Pacific jetstream collides at the Rockies, it may via complicated mechanisms (aka the Rossby waves mentioned above) cause amplification in the flow toward Europe, causing blocking to form. GWO orbit explained The GWO has a cyclical nature. This means that the GWO undergoes a kind of repetitive pattern, which can be explained by a circle diagram. Analogous to the MJO, the GWO has been divided in 8 phases, each with its own characteristics. All these phases are basically a follow-up of the phase before. The GWO orbit can be best seen as a measure for the total amount of AAM in the atmosphere. Below is the GWO orbit diagram with a brief explanation of what happens at every phase. Visualization of the GWO orbit In phase 1, negative mountain torque removes AAM from the atmosphere. The longer the GWO stays there, the lower the amount of AAM becomes in the atmosphere. This can be thought of a Jetstream colliding at a large mountain range Phase 2 and 3 generally describe low AAM values in the atmosphere (which is on average also occurring according to the conceptual model described above). In phase 4 and 5, positive mountain torque adds AAM to the atmosphere. The longer the GWO remains in that position, the higher the amount of AAM becomes in the atmosphere. Finally, phase 6 and 7 indicate high levels of AAM in the atmosphere. Concluding remarks There is much more that can be told about the GWO (and many other parameters), but that is for a later time! Any help or corrections in the explanation are greatly appreciated. Also, I hope many people will be willing to contribute to this thread! Here’s hoping that this will become a fruitful thread and a learning place for many! Useful links In the end, a list of links which could help for teleconnections are given here: GWO forecast: http://www.atmos.albany.edu/student/nschiral/gwo.html GWO composites: http://www.atmos.albany.edu/student/nschiral/comp.html MJO forecasts: http://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/mjo.shtml MJO composites: http://www.americanwx.com/raleighwx/MJO/MJO.html Update on tropical weather (expert assessment on tropical convection, including the MJO, great link): http://www.cpc.ncep.noaa.gov/products/precip/CWlink/ghazards/ ECMWF stratosphere forecast: http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/ Stratosphere updates: https://forum.netweather.tv/topic/81567-stratosphere-temperature-watch-20142015/ GWO further reading: http://www.esrl.noaa.gov/psd/map/clim/gwo.htm Sources: https://www.meted.ucar.edu/ http://www.esrl.noaa.gov/psd/map/clim/test_maproom.html
  3. Around this time of year I often search out new papers to assist in winter forecasting. However, quite often I lose the links to these papers by the time winter arrives. So, I think it makes sense to have a drop off zone for these type of papers that I and others come across. Please post in here any abstracts or PDF links that you may find of interest. A brief description of the paper would be most welcome. ( No climate change papers please)
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