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Found 135 results

  1. Links Section In This Post, below the intro. I have been recently asked to start a thread, to talk about weather teleconnections and similar topics. This is often a topic not very well discussed on other weather places, and places like Twitter. We have a number of experts, enthusiasts, and meteorologists, who are knowledgeable in this area. So this is a thread for technical discussion about the teleconnections, etc, as well as a place for questions about these topics. We need to start talking about these climate drivers more, as they are the key to unlocking medium-long term forecasts. We are making a place for technical discussion about these factors away from the main thread/s. So this thread is born. Teleconnections that could be up for discussion are: MJO, AAM/GWO, NAO, RRWT, NP jet, Mountain & Frictional Torques, AO/AAO, ENSO, IOD, AMO, SSTs in general, SOI, QBO, the Stratosphere, etc. Feel free to talk about related topics, but stick to this general topic. I encourage all posters to discuss and pose questions relating to the topic, and keep it a relaxed atmosphere. Any questions, just PM me or comment here. Hope we can make this work Links Section ERSL Link, Up to 24 hours behind. GWO 90 day Victor Gensini Site. http://atlas.niu.edu/gwo/ Features Total AAM, Bias Corrected Rel AAM GEFS, CFS GWO Forecast. He stated he is soon to add torque products. Nick Schraldi GWO Site http://www.atmos.albany.edu/student/nschiral/gwo.html Non-Bias Corrected GEFS GWO forecast. Michael Ventrice http://mikeventrice.weebly.com/hovmollers.html Hovmoller from MV, to help spot AAM trends and patterns. GEFS. Carl Schreck https://ncics.org/portfolio/monitor/mjo/ More Hovmollers and other tropical charts to spot trends in the AAM. CFS forecast. NPJ Phase Diagrams/Albany http://www.atmos.albany.edu/facstaff/awinters/realtime/Deterministic_NPJPD.php Shows a GEFS forecast and observation of NP jetstream, which is largely controlled by the AAM. MJO Composites: http://www.atmos.albany.edu/facstaff/roundy/waves/rmmcyc/index200reg.html
  2. The Global Wind Oscillation and its Impact on Southwest Michghan Severe Storms Authors: William Marino Published: 2016 (exact date not shown) Presentation Summary: • What is the Global Wind Oscillation (GWO) • Relating the GWO to Southwest Michigan severe storm events. • Trends in Severe storm frequency over Southwest Lower Michigan Link to presentation (slides only): https://www.weather.gov/media/grr/GLOM2015/Presentations/Marino_GWOSevereStorms.pdf I'm trying to find the full presentation and will edit this entry if I locate it.
  3. On the Seasonality of the El Niño Teleconnection to the Amundsen Sea Region Authors: Yu Yeung Scott Yiu and Amanda C. Maycocka Published: 11th July, 2019 Abstract: The Amundsen Sea low (ASL) is a quasi-stationary low pressure system that affects climate in West Antarctica. Previous studies have shown that El Niño–Southern Oscillation (ENSO) modulates the position and strength of the ASL with the strongest teleconnection found in austral winter despite the amplitude of ENSO events generally being largest in austral autumn/summer. This study investigates the mechanisms behind the seasonality of the El Niño teleconnection to the Amundsen Sea region (ASR) using experiments with the HadGEM3 climate model forced with an idealized fixed El Niño sea surface temperature anomaly present throughout the year. The seasonality of the El Niño–ASR teleconnection is found to originate from seasonal differences in the large-scale zonal winds in the South Pacific sector. In austral winter, the region of strong absolute vorticity near ~30°S associated with the subtropical jet, in combination with the changes to upper-tropospheric divergence due to the El Niño perturbation, acts as an anomalous Rossby wave source that is largely absent in austral summer. Furthermore, in austral summer the poleward propagation of tropically sourced Rossby waves into the ASR is inhibited by the strong polar front jet in the South Pacific sector, which leads to Rossby wave reflection away from the ASR. In austral winter, Rossby waves are able to propagate into the ASR, forming part of the Pacific South America pattern. The lack of the Rossby wave source in the tropical Pacific and the absence of favorable conditions for wave propagation explains the weaker El Niño–ASR teleconnection in austral summer compared to austral winter. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-18-0813.1
  4. On the Linearity of the Stratospheric and Euro-Atlantic Sector Response to ENSO Authors: Paloma Trascasa-Castro, Yu Yeung Scott YiuD and Jennifer K. Fletcher Published: 6th September, 2019 Abstract: The dependence of the winter stratospheric and Euro-Atlantic climate response on ENSO amplitude is investigated using the HadGEM3 model. Experiments are performed with imposed east Pacific sea surface temperature perturbations corresponding to Niño-3.4 anomalies of ±0.75, 1.5, 2.25, and 3.0 K. In the North Pacific, El Niño (EN) deepens and shifts the Aleutian low eastward, while the equivalent magnitude La Niña (LN) perturbations drive anomalies of opposite sign that are around 4 times weaker. The muted North Pacific response to LN can be traced back to the weaker response of tropical convection and the associated anomalous Rossby wave source. The EN perturbations weaken the Arctic polar vortex, with the winter mean zonal mean zonal wind at 60°N and 10 hPa decreasing approximately linearly with Niño-3.4 anomaly by around −3.6 m s−1 K−1. For the strongest EN case (+3 K), the frequency of sudden stratospheric warmings (SSWs) increases by ~60% compared to the control experiment. Hence the results do not support a saturation of the stratospheric pathway for strong EN as suggested in previous literature. The equivalent amplitude LN perturbations cause a weak strengthening of the polar vortex and no substantial change in SSW frequency, in contrast to some reanalysis-based studies. EN induces a negative North Atlantic Oscillation (NAO) index throughout boreal winter, which increases approximately linearly with the Niño-3.4 anomaly by around −0.6 standard deviations K−1. Only the response to the strongest LN perturbations projects onto a weak positive NAO in November, suggesting that the mechanism for the Euro-Atlantic response to LN may be distinct from EN. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-18-0746.1
  5. Dominant Covarying Climate Signals in the Southern Ocean and Antarctic Sea Ice Influence during the Last Three Decades Authors: D. Cerrone Published online: 6th April, 2017 Abstract: A composite dataset (comprising geopotential height, sea surface temperature, zonal and meridional surface winds, precipitation, cloud cover, surface air temperature, latent plus sensible heat fluxes, and sea ice concentration) has been investigated with the aim of revealing the dominant time scales of variability from 1982 to 2013. Three covarying climate signals associated with variations in the sea ice distribution around Antarctica have been detected through the application of the multiple-taper method with singular value decomposition (MTM-SVD). Features of the established patterns of variation over the Southern Hemisphere extratropics have been identified in each of these three climate signals in the form of coupled or individual oscillations. The climate patterns considered here are the southern annular mode (SAM), the Pacific–South American (PSA) teleconnection, the semiannual oscillation (SAO), and the zonal wavenumber-3 (ZW3) mode. It is shown that most of the sea ice temporal variance is concentrated at the quasi-triennial scale resulting from the constructive superposition of the PSA and ZW3 patterns. In addition, the combination of the SAM and SAO patterns is found to promote the interannual sea ice variations underlying a general change in the Southern Ocean atmospheric and oceanic circulations. These two modes of variability are also found to be consistent with the occurrence of the positive SAM/negative PSA (SAM+/PSA−) or negative SAM/positive PSA (SAM−/PSA+) combinations, which could have favored the cooling of the sub-Antarctic region and important changes in the Antarctic sea ice distribution since 2000. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-16-0439.1
  6. Atmospheric Patterns over the Antarctic Peninsula Authors: Sergi Gonzalez, Fransisco Vasallo, Cayetana Recio-Blitz, Jose A. Guljarro and Jesus Riesco Published online: 4th April, 2018 Abstract: Using clustering analysis for the sea level pressure field of the ERA-Interim reanalysis between 1979 and 2016, five synoptic pressure patterns have been obtained for the Drake area and Antarctic Peninsula (AP) region (45°–75°S, 20°–120°W), and the resulting daily series has been made available to the scientific community. The five patterns have been named according to their most important features as follows: low over the Weddell Sea (LWS), low over the Amundsen and Bellingshausen Seas (LAB), low over the Drake Passage (LDP), zonal flow over the Drake Passage (ZDP), and ridge over the Antarctic Peninsula (RAP). Each atmospheric pattern is described after analyzing its development and evolution. A frequency analysis shows that the five atmospheric patterns present a similar annual frequency but a large seasonal variability. The transitions from one pattern to another tend to follow a cycle in which synoptic atmospheric waves are displaced eastward by a quarter wavelength. Four of the five atmospheric patterns (all except RAP) are very influenced by the southern annular mode (SAM); however, only LAB and LWS are influenced to some degree by ENSO. The occurrence of the LAB pattern presents a positive trend showing agreement with other studies that indicate an enhancement of the Amundsen–Bellingshausen Seas low. Finally, atmospheric circulation patterns have been related to the airmass advection and precipitation in Livingston Island, showing the potential application for studying the changes in the surface mass balance on the AP cryosphere. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-17-0598.1
  7. The Climate of the Antarctic Peninsula during the Twentieth Century: Evidence from Ice Cores Authors: Elizabeth R. Thomas and Dieter R. Tetzner Published online: 5th November, 2018 Abstract: The Antarctic Peninsula (AP) is a region of special climatological interest. The late twentieth century has been a period of warming surface temperatures, enhanced mass loss from melting glaciers and increased snowfall, which have a direct and measurable impact on global sea levels. However, the observational period for Antarctica is short. Observational records only began in the 1940s and much of our understanding of the wider spatial climate variability and glacial dynamics is limited to the satellite era (post 1979). Proxy records, such as those from ice cores, provide an invaluable tool to place these recent changes in context of the past few hundred years, allowing us to investigate climate variability over the entire twentieth century and beyond. In this chapter we review the climate of the AP during the twentieth century, as captured by the instrumental records, and extend our understanding of climate variability over the twentieth century based on climate proxies contained in ice cores. For this study we focus on stable water isotopes and snow accumulation and how they are influenced by changes in atmospheric circulation and sea ice conditions. Link to full paper: https://www.intechopen.com/books/antarctica-a-key-to-global-change/the-climate-of-the-antarctic-peninsula-during-the-twentieth-century-evidence-from-ice-cores
  8. The North Pacific Pacemaker Effect on Historical ENSO and Its Mechanisms Authors: Dillon J. Amaya Published online: 11th October, 2019 Abstract: Studies have indicated that North Pacific sea surface temperature (SST) variability can significantly modulate El Niño–Southern Oscillation (ENSO), but there has been little effort to put extratropical–tropical interactions into the context of historical events. To quantify the role of the North Pacific in pacing the timing and magnitude of observed ENSO, we use a fully coupled climate model to produce an ensemble of North Pacific Ocean–Global Atmosphere (nPOGA) SST pacemaker simulations. In nPOGA, SST anomalies are restored back to observations in the North Pacific (>15°N) but are free to evolve throughout the rest of the globe. We find that the North Pacific SST has significantly influenced observed ENSO variability, accounting for approximately 15% of the total variance in boreal fall and winter. The connection between the North and tropical Pacific arises from two physical pathways: 1) a wind–evaporation–SST (WES) propagating mechanism, and 2) a Gill-like atmospheric response associated with anomalous deep convection in boreal summer and fall, which we refer to as the summer deep convection (SDC) response. The SDC response accounts for 25% of the observed zonal wind variability around the equatorial date line. On an event-by-event basis, nPOGA most closely reproduces the 2014/15 and the 2015/16 El Niños. In particular, we show that the 2015 Pacific meridional mode event increased wind forcing along the equator by 20%, potentially contributing to the extreme nature of the 2015/16 El Niño. Our results illustrate the significant role of extratropical noise in pacing the initiation and magnitude of ENSO events and may improve the predictability of ENSO on seasonal time scales. Link to full paper: This paper is behind an AMS paywall but I managed obtain the editor's pre-submission final draft version via the University of Exeter (which by coincidence is just 10 miles from where I live!): https://pdfs.semanticscholar.org/9f07/cfd3814de0849f85741f6ac2ef700ab60117.pdf
  9. Role of Stochastic Atmospheric Forcing in Tropical Pacific Decadal Variability and ENSO Modulation - Presentation 98th American Meteorological Society Annual Meeting:, held in Austin, Texas from 6th to 11th January, 2018 Presenters: Tianyi Sun and Y. M. Okumura Presentation Date: 8th January, 2018 Summary: The analysis of a millennium-long control simulation of the Community Climate System Model version 4 (CCSM4) suggests that the amplitude and other properties of El Niño-Southern Oscillation (ENSO) vary significantly on decadal-interdecadal time scales in association with changes in the tropical Pacific background state. Intriguingly, the patterns of tropical Pacific decadal variability (TPDV) related to the ENSO modulation in CCSM4 are reproduced to some degree in a control simulation of the atmospheric component (CAM4) coupled to a slab ocean model (SOM). In both CCSM4 and CAM4-SOM, the extratropical atmospheric circulation anomalies associated with TPDV project onto the leading modes of internal atmospheric variability over the North and South Pacific, namely, the North Pacific oscillation (NPO) and Pacific South-American (PSA) patterns. This result suggests that TPDV driven by stochastic atmospheric forcing interacts with the equatorial ocean dynamics and modulates ENSO. To test this hypothesis, we conduct a set of CCSM4 experiments by imposing surface heat flux anomalies associated with the NPO and PSA patterns over the North and South Pacific, respectively. The results show that the PSA experiment induces a basin-wide sea surface temperature (SST) anomaly pattern that resembles the observed interdecadal Pacific oscillation although the forcing is confined to the South Pacific. However, the corresponding wind anomalies induce negative feedback through oceanic processes, resulting in a weak response in the equatorial Pacific. The influence of the NPO pattern, on the other hand, is mostly confined to the North Pacific with small SST changes over the tropical Pacific. Both the NPO and PSA experiments show significant changes in the relative frequency of El Niño and La Niña events, in support of the hypothesized mechanism of ENSO modulation. Link to presentation video (14 minutes): https://ams.confex.com/ams/98Annual/videogateway.cgi/id/42668?recordingid=42668&uniqueid=Paper327563&entry_password=null Link to full conference program: https://ams.confex.com/ams/98Annual/webprogram/meeting.html The authors followed up with their research paper which was published on 14th June, 2019 but is still behind an AMS paywall. Link to paper: https://journals.ametsoc.org/doi/10.1175/JCLI-D-18-0536.1
  10. Decadal Variability of the ENSO Teleconnection to the High-Latitude South Pacific Governed by Coupling with the Southern Annular Mode Authors: Ryan L. Fogt and David H. Bromwich Published: 15th March, 2006 Abstract: Decadal variability of the El Niño–Southern Oscillation (ENSO) teleconnection to the high-latitude South Pacific is examined by correlating the European Centre for Medium-Range Weather Forecasts (ECMWF) 40-yr Re-Analysis (ERA-40) and observations with the Southern Oscillation index (SOI) over the last two decades. There is a distinct annual contrast between the 1980s and the 1990s, with the strong teleconnection in the 1990s being explained by an enhanced response during austral spring. Geopotential height anomaly composites constructed during the peak ENSO seasons also demonstrate the decadal variability. Empirical orthogonal function (EOF) analysis reveals that the 1980s September–November (SON) teleconnection is weak due to the interference between the Pacific–South American (PSA) pattern associated with ENSO and the Southern Annular Mode (SAM). An in-phase relationship between these two modes during SON in the 1990s amplifies the height and pressure anomalies in the South Pacific, producing the strong teleconnections seen in the correlation and composite analyses. The in-phase relationship between the tropical and high-latitude forcing also exists in December–February (DJF) during the 1980s and 1990s. These results suggest that natural climate variability plays an important role in the variability of SAM, in agreement with a growing body of literature. Additionally, the significantly positive correlation between ENSO and SAM only during times of strong teleconnection suggests that both the Tropics and the high latitudes need to work together in order for ENSO to strongly influence Antarctic climate. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/JCLI3671.1
  11. The Interconnected Global Climate System—A Review of Tropical–Polar Teleconnections Authors: Xiaojun Yuan, Michael R. Kaplan, and Mark A. Cane Published: 29th June, 2018 Abstract: This paper summarizes advances in research on tropical–polar teleconnections, made roughly over the last decade. Elucidating El Niño–Southern Oscillation (ENSO) impacts on high latitudes has remained an important focus along different lines of inquiry. Tropical to polar connections have also been discovered at the intraseasonal time scale, associated with Madden–Julian oscillations (MJOs). On the time scale of decades, changes in MJO phases can result in temperature and sea ice changes in the polar regions of both hemispheres. Moreover, the long-term changes in SST of the western tropical Pacific, tropical Atlantic, and North Atlantic Ocean have been linked to the rapid winter warming around the Antarctic Peninsula, while SST changes in the central tropical Pacific have been linked to the warming in West Antarctica. Rossby wave trains emanating from the tropics remain the key mechanism for tropical and polar teleconnections from intraseasonal to decadal time scales. ENSO-related tropical SST anomalies affect higher-latitude annular modes by modulating mean zonal winds in both the subtropics and midlatitudes. Recent studies have also revealed the details of the interactions between the Rossby wave and atmospheric circulations in high latitudes. We also review some of the hypothesized connections between the tropics and poles in the past, including times when the climate was fundamentally different from present day especially given a larger-than-present-day global cryosphere. In addition to atmospheric Rossby waves forced from the tropics, large polar temperature changes and amplification, in part associated with variability in orbital configuration and solar irradiance, affected the low–high-latitude connections. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-16-0637.1
  12. The relationship between the El Niño/La Niña cycle and the transition chains of four atmospheric oscillations. Part I: The Four Oscillations Authors: Jingbei Peng, Lieting Chen and Qingyun Zhang Published: 8th February, 2014 Abstract: The first leading modes of the interannual variations in low-level circulation over the North and South Pacific are the Northern Oscillation (NO) and Southern Oscillation (SO), which are oscillations in sea level pressure anomalies (SLPAs) between the eastern and western Pacific Ocean. The second leading modes are the North Pacific Oscillation (NPO) and the Antarctic Oscillation (AAO), which reflect oscillations between the subtropics and the high and middle latitudes. The transition chains of these four oscillations were investigated using the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis data. The general pattern of the transition chain between the NO and NPO was from the negative phase of the NO (NO−) to the positive phase of the NPO (NPO+), then from NO+ to NPO− to NO−. The whole transition chain took about 4–6 years. The general pattern and period of the transition between the SO and AAO were similar to those between the NO and NPO. In addition, the transition chains between the NO and NPO, and the SO and AAO, were almost simultaneous. The transition chains of the four oscillations were found to be closely connected, with the eastward propagations of SLPAs occurring along both sides of the Equator. Link to full paper: This is behind a paywall and yet part is available! The ResearchGate site just shows the abstract with a "download request" option:: https://www.researchgate.net/publication/260527686_The_Relationship_between_the_El_NinoLa_Nina_Cycle_and_the_Transition_Chains_of_Four_Atmospheric_Oscillations_Part_I_The_Four_Oscillations There is a link to the original Springer Link site (where the paywall is): https://link.springer.com/article/10.1007%2Fs00376-013-2275-0 The introduction is there to tempt us further! If/when this paper becomes free access, I will update the link. Curiously part 1 appears top have been published nearly a year after part 2! I assume that the original version was revised?
  13. The Teleconnection of El Niño Southern Oscillation to the Stratosphere Authors: Daniela I.V. Domeisen, Chaim I. Garfinkel and Amy H. Butler Published: 30th November, 2018 Abstract: El Niño and La Niña events in the tropical Pacific have significant and disrupting impacts on the global atmospheric and oceanic circulation. El Niño Southern Oscillation (ENSO) impacts also extend above the troposphere, affecting the strength and variability of the stratospheric polar vortex in the high latitudes of both hemispheres, as well as the composition and circulation of the tropical stratosphere. El Niño events are associated with a warming and weakening of the polar vortex in the polar stratosphere of both hemispheres, while a cooling can be observed in the tropical lower stratosphere. These impacts are linked by a strengthened Brewer‐Dobson circulation. Anomalous upward wave propagation is observed in the extratropics of both hemispheres. For La Niña, these anomalies are often opposite. The stratosphere in turn affects surface weather and climate over large areas of the globe. Since these surface impacts are long‐lived, the changes in the stratosphere can lead to improved surface predictions on time scales of weeks to months. Over the past decade, our understanding of the mechanisms through which ENSO can drive impacts remote from the tropical Pacific has improved. This study reviews the possible mechanisms connecting ENSO to the stratosphere in the tropics and the extratropics of both hemispheres while also considering open questions, including nonlinearities in the teleconnections, the role of ENSO diversity, and the impacts of climate change and variability. Link to full paper: https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2018RG000596
  14. Weakening Atlantic Niño–Pacific connection under greenhouse warming Authors: Fan Jia, Wenju Cai, Lixin Wu, Bolan Gan, Guojian Wang, Fred Kucharski, Ping Chang and Noel Keenlyside Published: 21st August, 2019 Abstract: Sea surface temperature variability in the equatorial eastern Atlantic, which is referred to as an Atlantic Niño (Niña) at its warm (cold) phase and peaks in boreal summer, dominates the interannual variability in the equatorial Atlantic. By strengthening of the Walker circulation, an Atlantic Niño favors a Pacific La Niña, which matures in boreal winter, providing a precursory memory for El Niño–Southern Oscillation (ENSO) predictability. How this Atlantic impact responds to greenhouse warming is unclear. Here, we show that greenhouse warming leads to a weakened influence from the Atlantic Niño/Niña on the Pacific ENSO. In response to anomalous equatorial Atlantic heating, ascending over the equatorial Atlantic is weaker due to an increased tropospheric stability in the mean climate, resulting in a weaker impact on the Pacific Ocean. Thus, as greenhouse warming continues, Pacific ENSO is projected to be less affected by the Atlantic Niño/Niña and more challenging to predict. Link to full paper: https://advances.sciencemag.org/content/5/8/eaax4111
  15. A Teleconnection between the West Siberian Plain and the ENSO Region Authors: Stefan Liess, Saurabh Agrawal, Snigdhansu Chatterjee and Vipin Kumar Published: 19th December, 2016 Abstract: The Walker circulation is linked to extratropical waves that are deflected from the Northern Hemisphere polar regions and travel southeastward over central Asia toward the western Pacific warm pool during northern winter. The wave pattern resembles the east Atlantic–west Russia pattern and influences the El Niño–Southern Oscillation (ENSO) region. A tripole pattern between the West Siberian Plain and the two centers of action of ENSO indicates that the background state of ENSO with respect to global sea level pressure (SLP) has a significant negative correlation to the West Siberian Plain. The correlation with the background state, which is defined by the sum of the two centers of action of ENSO, is higher than each of the pairwise correlations with either of the ENSO centers alone. The centers are defined with a clustering algorithm that detects regions with similar characteristics. The normalized monthly SLP time series for the two centers of ENSO (around Darwin, Australia, and Tahiti) are area averaged, and the sum of both regions is considered as the background state of ENSO. This wave train can be detected throughout the troposphere and the lower stratosphere. Its origins can be traced back to Rossby wave activity triggered by convection over the subtropical North Atlantic that emanates wave activity toward the West Siberian Plain. The same wave train also propagates to the central Pacific Ocean around Tahiti and can be used to predict the background state over the ENSO region. This background state also modifies the subtropical bridge between tropical eastern Pacific and subtropical North Atlantic leading to a circumglobal wave train. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-15-0884.1
  16. Pacific decadal climate variability: Indices, patterns and tropical-extratropical interactions Authors: Benjamin J. Henley Published: 1st August, 2017 Abstract: Pacific decadal variability (PDV) plays a critical role in the climate system. Here I present a review of indices and patterns of decadal climate variability in the Pacific from observations and palaeoclimate reconstructions. I examine the spatial characteristics of Pacific sea surface temperature variability and the metrics used to track observations of PDV. I find commonalities between the PDV patterns, the Interdecadal Pacific Oscillation (IPO) and its North and South Pacific counterparts, the Pacific Decadal and South Pacific Decadal Oscillations (PDO and SPDO). I present a tool to provide probabilistic quantification of the recent state of the IPO, and use the tool to provide reliable estimates of IPO state up to 2 years prior to the present. The tool indicates a probability of 80–90% that the IPO remained in its negative state until 2014–2015. I review palaeoclimate reconstructions of the IPO and PDO, and outline advances and challenges in our pre-instrumental understanding of PDV. I draw attention to a Pacific-wide tropical-extratropical mechanism that suggests that the cool and warm phases of PDV are not driven by tropical or extratropical variability alone, but are instead the result of continuous tropical-extratropical interactions on decadal timescales. I conclude by noting key sources of remaining uncertainty and emphasising the need to better understand decadal variability. This will occur through continual improvements in observations, an expansion of palaeoclimate exploration and data collection, and renewed efforts in model development. Link to full paper: https://minerva-access.unimelb.edu.au/bitstream/handle/11343/225013/Henley_PacificReview.pdf;jsessionid=04CCB1825E33DC0199ED2F8E1D2288A4?sequence=1
  17. The role of the stratosphere in the European climate response to El Niño Authors: S. Ineson and A. A. Scaife First Published: 7th December, 2008 Abstract: El Niño/Southern Oscillation (ENSO) is the largest natural interannual climate signal in the tropics; oscillations between warm El Niño and cold La Niña phases occur every few years. The effects are felt not only in the centre of action, the tropical Pacific region, but around the globe. Observational studies show a clear response in European climate to ENSO in late winter. However, the underlying mechanisms of the link are not yet understood. Here we use a general circulation model of the atmosphere, that has been extended into the upper atmospheric layers, to provide end-to-end evidence for a global teleconnection pathway from the Pacific region to Europe via the stratosphere. We present evidence for an active stratospheric role in the transition to cold conditions in northern Europe and mild conditions in southern Europe in late winter during El Niño years. In our experiments, this mechanism is restricted to years when stratospheric sudden warmings occur. The response in European surface climate to the El Niño signal is large enough to be useful for seasonal forecasting. Link to full paper: The "Nature GeoScience Link" access is still behind a paywall ( https://www.nature.com/articles/ngeo381 ) but there is now a downloadable personal pdf version via this ResearchGate link: https://www.researchgate.net/publication/240493807_The_role_of_the_stratosphere_in_the_European_climate_response_to_El_No
  18. Review of Tropical‐Extratropical Teleconnections on Intraseasonal Time Scales Authors: Cristiana Stan, David M. Straus, Jorgen S. Frederiksen, Hai Lin, Eric D. Maloney and Courtney Schumacher First Published: 12th September, 2017 Abstract: The interactions and teleconnections between the tropical and midlatitude regions on intraseasonal time scales are an important modulator of tropical and extratropical circulation anomalies and their associated weather patterns. These interactions arise due to the impact of the tropics on the extratropics, the impact of the midlatitudes on the tropics, and two‐way interactions between the regions. Observational evidence, as well as theoretical studies with models of complexity ranging from the linear barotropic framework to intricate Earth system models, suggest the involvement of a myriad of processes and mechanisms in generating and maintaining these interconnections. At this stage, our understanding of these teleconnections is primarily a collection of concepts; a comprehensive theoretical framework has yet to be established. These intraseasonal teleconnections are increasingly recognized as an untapped source of potential subseasonal predictability. However, the complexity and diversity of mechanisms associated with these teleconnections, along with the lack of a conceptual framework to relate them, prevent this potential predictability from being translated into realized forecast skill. This review synthesizes our progress in understanding the observed characteristics of intraseasonal tropical‐extratropical interactions and their associated mechanisms, identifies the significant gaps in this understanding, and recommends new research endeavors to address the remaining challenges. Link to full paper: https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2016RG000538
  19. Relationship between Tropical Pacific SST and global atmospheric angular momentum in coupled models Authors: Huei−Ping Huang, Matthew Newman, Richard Seager, Yochanan Kushnir and Participating CMIP2+ Modeling Groups First Published: January 2004 Abstract: The sensitivity parameter S1 = ∆AAM/∆SST, where ∆AAM and ∆SST represent the anomalies of global atmospheric angular momentum (AAM) and tropical Pacific sea surface temperature (SST) in the NINO3.4 region, is compared for the CMIP2+ coupled models. The parameter quantifies the strength of atmospheric zonal mean zonal wind response to SST anomaly in the equatorial Pacific, an important process for the climate system. Although the simulated ∆AAM and ∆SST are found to exhibit great disparity, their ratios agree better among the coupled models (and with observation) with no significant outliers. This indicates that the processes that connect the AAM anomaly to tropical SST anomaly are not sensitive to the base SST and the detail of convective heating and are relatively easy to reproduce by the coupled models. Through this robust ∆SST−∆AAM relationship, the model bias in tropical Pacific SST manifests itself in the bias in atmospheric angular momentum. The value of S1 for an atmospheric model forced by observed SST is close to that for a coupled model with a similar atmospheric component, suggesting that the ∆SST− ∆AAM relationship is dominated by a one−way influence of the former forcing the latter. The physical basis for the ∆SST−∆AAM relationship is explored using a statistical equilibrium argument that links ∆SST to the anomaly of tropical tropospheric temperature. The resulting meridional gradient of tropospheric temperature is then linked to the change in zonal wind in the subtropical jets, the main contributor to ∆AAM, by thermal wind balance. Link to Paper: https://pcmdi.llnl.gov/mips/cmip/cmip_abstracts/huang04.pdf?id=95 Credit goes to Tom @Isotherm for finding this paper - thank you.
  20. Seasonal and Regional Variations of Long-Term Changes in Upper-Tropospheric Jets from Reanalyses Authors: Gloria L. Manney and Michaela I. Hegglin First Published: September 15th, 2017 Published on line: December 19th, 2017 Abstract: Long-term changes in upper-tropospheric jet latitude, altitude, and strength are assessed for 1980–2014 using five modern reanalyses: MERRA, MERRA-2, ERA-Interim, JRA-55, and NCEP CFSR. Changes are computed from jet locations evaluated daily at each longitude to analyze regional and seasonal variations. The changes in subtropical and polar (eddy driven) jets are evaluated separately. Good agreement among the reanalyses in many regions and seasons provides confidence in the robustness of the diagnosed trends. Jet shifts show strong regional and seasonal variations, resulting in changes that are not robust in zonal or annual means. Robust changes in the subtropical jet indicate tropical widening over Africa except during Northern Hemisphere (NH) spring, and tropical narrowing over the eastern Pacific in NH winter. The Southern Hemisphere (SH) polar jet shows a robust poleward shift, while the NH polar jet shifts equatorward in most regions/seasons. Both subtropical and polar jet altitudes typically increase; these changes are more robust in the NH than in the SH. Subtropical jet wind speeds have generally increased in winter and decreased in summer, whereas polar jet wind speeds have weakened (strengthened) over Africa and eastern Asia (elsewhere) during winter in both hemispheres. The Asian monsoon has increased in area and appears to have shifted slightly westward toward Africa. The results herein highlight the importance of understanding regional and seasonal variations when quantifying long-term changes in jet locations, the mechanisms for those changes, and their potential human impacts. Comparison of multiple reanalyses is a valuable tool for assessing the robustness of jet changes. Link to Paper: https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-17-0303.1
  21. The key role of background sea surface temperature over the cold tongue in asymmetric responses of the Arctic stratosphere to El Niño–Southern Oscillation Authors: Fei Xie, Xin Zhou, Jianping Li, Cheng Sun, Juan Feng and Xuan Ma Published: Nov 2018 Abstract: The response of the Arctic stratosphere to El Niño activity is strong but the response to La Niña activity is relatively weak. The asymmetric responses of Arctic stratosphere to El Niño and La Niña events are thought to be caused by asymmetric El Niño–Southern Oscillation (ENSO) teleconnections. Here, we suggest that the background sea surface temperature (SST) over cold tongue of tropical eastern Pacific may be an important contributor to the asymmetric ENSO teleconnections. The atmosphere is very sensitive to tropical SST variations in the range of 26 °C–30 °C. During El Niño events, the background SST over cold tongue plus El Niño SST anomalies typically falls into the range. Under these conditions, the atmospheric response to El Niño SST anomalies is strong. During La Niña events, the background SST plus La Niña SST anomalies is typically below the range, which leads to a weak response of the atmosphere to SST anomalies. The proposed mechanism is well supported by simulations. Link to full paper: http://iopscience.iop.org/article/10.1088/1748-9326/aae79b/meta
  22. Global Warming and ENSO – A “Helter-Skelter” Atmosphere Authors: Daphne Thompson (for WDT) Published: 11th December, 2017 Abstract: (None but I extracted this from the text): The purpose of this article is to make an effort to illustrate circulation impacts due to climate change, and give some high-level observational evidence of a La Niña-like response due to global warming, including at present. From another perspective, the ongoing El Niño could be contributing to La Niña aspects of the current atmospheric circulation given that it may be amplifying the present increase in the global mean temperature. Emphasis is then placed on the relevancy of climate change to subseasonal forecasting, including the present 16-30 day outlooks issued by WDT. The “global warming-La Niña” connection has been gaining some recognition in a few very recent publications in the refereed literature, as well as in on-line blogs written by well-respected scientists. The reader is encouraged to do a search. No attempt will be made to get into the complicated issues of the causes of climate change (including global warming) other than described above Link to full paper: https://blog.weatherops.com/global-warming-and-enso-a-helter-skelter-atmosphere Credit goes to Tams @Tamara for finding this paper - thank you.
  23. Studies of atmospheric angular momentum Authors: NOAA, Climate Diagnostics Center, Science Review Published: 25th/26th July, 2001 Chapter 4: Empirical and Process Studies Introduction to chapter 4, part 3: Atmospheric angular momentum (AAM) provides a convenient framework to study the role of mountains, surface wind stresses and various transport mechanisms in variability ranging from intraseasonal to interdecadal and beyond. Quantitative studies are feasible with current global assimilated datasets which show a good budget balance for global integrals, intraseasonal variations and during northern winter/spring. The budgets get much worse when gravity wave drag is included, if zonal integrals are considered or during summer/fall seasons. AAM is useful as an index of the large scale zonal flow since it is highly correlated with independent length-of-day measurements and with phenomena such as the QBO, ENSO, the MJO and possibly global warming. CDC scientists have examined several aspects of AAM variability, including: the link to MJO tropical convection, a linear model of global AAM and its torques, the global AAM budget imbalances due to gravity wave drag, the forcing for the semiannual seasonal component of AAM and the AAM response to global warming in an ensemble of coupled ocean-atmosphere model runs. CDC also monitors in real time the complete vertically integrated budget as part of its web-based maproom activities and distributes AAM and torque data to other researchers. Link to full paper: https://www.esrl.noaa.gov/psd/psd1/review/Chap04/sec3_body.html Link to Introduction to Chapter 4: https://www.esrl.noaa.gov/psd/psd1/review/Chap04/index.html Link to full Science Review: https://www.esrl.noaa.gov/psd/psd1/review/SciRev.pdf
  24. Where is ENSO stress balanced? Authors: Matthias Münnich and David Neelin First Published: 20th November, 2003 Published online: 14th April, 2004 Abstract: The zonal surface torque budget associated with the tropical wind stress anomalies during El Niño/Southern Oscillation is analyzed. Mountain and surface stress torques over South America are found to play a prominent role. Local momentum change is negligible for 6 month averages allowing the balance among regional contributions to the torque anomalies to be compared. During El Niño, eastward torque anomalies over the central equatorial Pacific are largely compensated by westward anomalies elsewhere in the equatorial band, notably over South America. Torque anomalies over South America and the Pacific in latitude bands north and south of the equator are both westward and are not compensated within the band, implying an export of eastward momentum to higher latitudes. Copyright © 2003 Royal Meteorological Society. Published by Elsevier Ltd. All rights reserved. Link to full paper: https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1016/j.atmoscilet.2003.11.001
  25. Observed Changes in the Lifetime and Amplitude of the MJO Associated with Interannual ENSO Sea Surface Temperature Anomalies Authors: Benjamin Pohl and Adrian J. Matthews Published: 1st June, 2007 Abstract: The Madden–Julian oscillation (MJO) is analyzed using the reanalysis zonal wind– and satellite outgoing longwave radiation–based indices of Wheeler and Hendon for the 1974–2005 period. The average lifetime of the MJO events varies with season (36 days for events whose central date occurs in December, and 48 days for events in September). The lifetime of the MJO in the equinoctial seasons (March–May and October–December) is also dependent on the state of El Niño–Southern Oscillation (ENSO). During October–December it is only 32 days under El Niño conditions, increasing to 48 days under La Niña conditions, with similar values in northern spring. This difference is due to faster eastward propagation of the MJO convective anomalies through the Maritime Continent and western Pacific during El Niño, consistent with theoretical arguments concerning equatorial wave speeds. The analysis is extended back to 1950 by using an alternative definition of the MJO based on just the zonal wind component of the Wheeler and Hendon indices. A rupture in the amplitude of the MJO is found in 1975, which is at the same time as the well-known rupture in the ENSO time series that has been associated with the Pacific decadal oscillation. The mean amplitude of the MJO is 16% larger in the postrupture (1976–2005) compared to the prerupture (1950–75) period. Before the 1975 rupture, the amplitude of the MJO is maximum (minimum) under El Niño (La Niña) conditions during northern winter, and minimum (maximum) under El Niño (La Niña) conditions during northern summer. After the rupture, this relationship disappears. When the MJO–ENSO relationship is analyzed using all-year-round data, or a shorter dataset (as in some previous studies), no relationship is found. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/JCLI4230.1 Credit goes to Eric @Webberweather for finding this paper - thank you.
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