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Found 37 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 Effect of QBO Phase on the Atmospheric Response to Projected Arctic Sea Ice Loss in Early Winter Authors: Zachary Labe, Yannick Peings and Gudrun Magnusdottir Published online: 24th June, 2019 Abstract: Recent modeling studies have shown an important role for stratosphere‐troposphere coupling in the large‐scale atmospheric response to Arctic sea ice loss. Evidence is growing that the Quasi‐biennial Oscillation (QBO) can contribute to or even mitigate teleconnections from surface forcing. Here, the influence of QBO phase on the atmospheric response to projected Arctic sea ice loss is examined using an atmospheric general circulation model with a well‐resolved stratosphere and a QBO prescribed from observations. The role of the QBO is determined by compositing seasons with easterly phase (QBO‐E) separately from seasons with westerly phase (QBO‐W). In response to the sea ice forcing in early winter, the polar vortex during QBO‐E weakens with strong stratosphere‐troposphere wave‐1 coupling and a negative Northern Annular Mode‐type response. At the surface, this results in more severe Siberian cold spells. For QBO‐W, the polar vortex strengthens in response to the sea ice forcing. Plain Language Summary: Rapid loss of Arctic sea ice area and thickness are key indicators of global climate change. Global climate models project further loss of Arctic sea ice through the end of the 21st century. How weather patterns and the jet stream will respond to this sudden loss of sea ice is still poorly understood. Here we use a series of climate model experiments to understand how the atmospheric response to sea ice loss is affected by alternating easterly and westerly winds in the tropical middle atmosphere, known as the Quasi‐biennial Oscillation. We show that the Quasi‐biennial Oscillation has an important role in understanding how weather patterns can respond to a decrease in sea ice. Link to full article: This new paper is still behind the AGU100 paywall - subscibers can access here: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019GL083095 Fortunately, Zach Labe has copied most of it to his own website - link here: https://sites.uci.edu/zlabe/qbo-and-arctic-sea-ice/ Before that Zach Labe made a poster presentation on this subject at the 20th Conference on Middle Atmosphere, Phoenix, AZ (Jan 2019): Link to Poster Charts: https://agu.confex.com/agu/fm18/meetingapp.cgi/Paper/399117 Link to presentation Summary: https://agu.confex.com/agu/fm18/meetingapp.cgi/Paper/399117. Link to 15 minute video: https://ams.confex.com/ams/2019Annual/videogateway.cgi/id/51083?recordingid=51083 Zach labe also presentented at the AGU Fall meeting in December 2018: https://agu.confex.com/agu/fm18/meetingapp.cgi/Paper/399117
  3. 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
  4. The importance of stratospheric initial conditions for winter North Atlantic Oscillation predictability and implications for the signal‐to‐noise paradox Authors: Christopher H. O'Reilly, Antje Weisheimer, Tim Woollings, Lesley J. Gray and Dave MacLeod Published: 12th October, 2018 Abstract: This study investigates the influence of atmospheric initial conditions on winter seasonal forecasts of the North Atlantic Oscillation (NAO). Hindcast (or reforecast) experiments – which differ only in their initial conditions – are performed over the period 1960–2009, using prescribed sea surface temperature (SST) and sea‐ice boundary conditions. The first experiment (“ERA‐40/Int IC”) is initialized using the ERA‐40 and ERA‐Interim reanalysis datasets, which assimilate upper‐air, satellite and surface observations; the second experiment (“ERA‐20C IC”) is initialized using the ERA‐20C reanalysis dataset, which assimilates only surface observations. The ensemble mean NAO skill is largest in ERA‐40/Int IC (r = 0.54), which is initialized with the superior reanalysis data. Moreover, ERA‐20C IC did not exhibit significantly more NAO hindcast skill (r = 0.38) than in a third experiment, which was initialized with incorrect (shuffled) initial conditions. The ERA‐40/Interim and ERA‐20C initial conditions differ substantially in the tropical stratosphere, where the quasi‐biennial oscillation (QBO) of zonal winds is not present in ERA‐20C. The QBO hindcasts are highly skilful in ERA‐40/Int IC – albeit with a somewhat weaker equatorial zonal wind amplitude in the lower stratosphere – but are incorrect in ERA‐20C IC, indicating that the QBO is responsible for the additional NAO hindcast skill; this is despite the model exhibiting a relatively weak teleconnection between the QBO and NAO. The influence of the QBO is further demonstrated by regressing out the QBO influence from each of the hindcast experiments, after which the difference in NAO hindcast skill between the experiments is negligible. Whilst ERA‐40/Int IC demonstrates a more skilful NAO hindcast, it appears to have a relatively weak predictable signal; this is the so‐called “signal‐to‐noise paradox” identified in previous studies. Diagnostically amplifying the (weak) QBO–NAO teleconnection increases the ensemble‐mean NAO signal with negligible impact on the NAO hindcast skill, after which the signal‐to‐noise problem seemingly disappears. Link to full paper: https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/qj.3413
  5. Sub-seasonal Predictability and the Stratosphere Authors: Amy Butler et al Published: 8th July, 2019 Abstract: The stratosphere and the troposphere are coupled in many ways. Because their interactions span days to weeks (or even longer), understanding these linkages and simulating them correctly in forecast models may provide a source of sub-seasonal to seasonal (S2S) prediction skill. This chapter reviews the tropical and extratropical coupling between the stratosphere and the troposphere and summarizes the most recent research showing how adequate simulation of the stratosphere may contribute to better prediction skill in the troposphere. Link to full paper: https://edwinpgerber.github.io/files/butler_etal-S2S-2019.pdf
  6. High‐latitude influence of the quasi‐biennial oscillation Authors: James A. Anstey and Theodore G. Shepherd Published: 28th March, 2013 Abstract: The interannual variability of the stratospheric winter polar vortex is correlated with the phase of the quasi‐biennial oscillation (QBO) of tropical stratospheric winds. This dynamical coupling between high and low latitudes, often referred to as the Holton–Tan effect, has been the subject of numerous observational and modelling studies, yet important questions regarding its mechanism remain unanswered. In particular it remains unclear which vertical levels of the QBO exert the strongest influence on the winter polar vortex, and how QBO–vortex coupling interacts with the effects of other sources of atmospheric interannual variability such as the 11‐year solar cycle or the El Niño Southern Oscillation. As stratosphere‐resolving general circulation models begin to resolve the QBO and represent its teleconnections with other parts of the climate system, it seems timely to summarize what is currently known about the QBO's high‐latitude influence. In this review article, we offer a synthesis of the modelling and observational analyses of QBO–vortex coupling that have appeared in the literature, and update the observational record. Link to full paper: https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/qj.2132
  7. Optimization of Gravity Wave Source Parameters for Improved Seasonal Prediction of the Quasi-Biennial Oscillation Authors: Cory A. Barton, John P. McCormack and Karl W. Hoppel Published: 9th September, 2019 Abstract: A methodology is presented for objectively optimizing nonorographic gravity wave source parameters to minimize forecast error for target regions and forecast lead times. In this study, we employ a high-altitude version of the Navy Global Environmental Model (NAVGEM-HA) to ascertain the forcing needed to minimize hindcast errors in the equatorial lower stratospheric zonal-mean zonal winds in order to improve forecasts of the quasi-biennial oscillation (QBO) over seasonal time scales. Because subgrid-scale wave effects play a large role in driving the QBO, this method leverages the nonorographic gravity wave drag (GWD) parameterization scheme to provide the necessary forcing. To better constrain the GWD source parameters, we utilize ensembles of NAVGEM-HA hindcasts over the 2014–16 period with perturbed source parameters and develop a cost function to minimize errors in the equatorial lower stratosphere compared to analysis. Thus, we may determine the set of GWD source parameters that yields a forecast state that most closely agrees with observed QBO winds over each optimization time interval. Results show that the source momentum flux and phase speed spectrum width are the most important parameters. The seasonal evolution of optimal parameter value, specifically a robust semiannual periodicity in the source strength, is also revealed. Changes in optimal source parameters with increasing forecast lead time are seen, as the GWD parameterization takes on a more active role as QBO driver at longer forecast lengths. Implementation of a semiannually varying source function at the equator provides RMS error improvement in QBO winds over the default constant value. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/JAS-D-19-0077.1
  8. Simulating the QBO in an Atmospheric General Circulation Model: Sensitivity to Resolved and Parameterized Forcing Authors: James A. Anstey, John F. Scinocca and Martin Keller Published: 3rd March, 2016 Abstract: The quasi-biennial oscillation (QBO) of tropical stratospheric zonal winds is simulated in an atmospheric general circulation model and its sensitivity to model parameters is explored. Vertical resolution in the lower tropical stratosphere finer than ≈1 km and sufficiently strong forcing by parameterized nonorographic gravity wave drag are both required for the model to exhibit a QBO-like oscillation. Coarser vertical resolution yields oscillations that are seasonally synchronized and driven mainly by gravity wave drag. As vertical resolution increases, wave forcing in the tropical lower stratosphere increases and seasonal synchronization is disrupted, allowing quasi-biennial periodicity to emerge. Seasonal synchronization could result from the form of wave dissipation assumed in the gravity wave parameterization, which allows downward influence by semiannual oscillation (SAO) winds, whereas dissipation of resolved waves is consistent with radiative damping and no downward influence. Parameterized wave drag is nevertheless required to generate a realistic QBO, effectively acting to amplify the relatively weaker mean-flow forcing by resolved waves. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/JAS-D-15-0099.1
  9. Constraints on Wave Drag Parameterization Schemes for Simulating the Quasi-Biennial Oscillation. Part II: Combined Effects of Gravity Waves and Equatorial Planetary Waves Authors: Lucy J. Campbell and Theodore G. Shepherd Published: 1st December, 2005 Abstract: This study examines the effect of combining equatorial planetary wave drag and gravity wave drag in a one-dimensional zonal mean model of the quasi-biennial oscillation (QBO). Several different combinations of planetary wave and gravity wave drag schemes are considered in the investigations, with the aim being to assess which aspects of the different schemes affect the nature of the modeled QBO. Results show that it is possible to generate a realistic-looking QBO with various combinations of drag from the two types of waves, but there are some constraints on the wave input spectra and amplitudes. For example, if the phase speeds of the gravity waves in the input spectrum are large relative to those of the equatorial planetary waves, critical level absorption of the equatorial planetary waves may occur. The resulting mean-wind oscillation, in that case, is driven almost exclusively by the gravity wave drag, with only a small contribution from the planetary waves at low levels. With an appropriate choice of wave input parameters, it is possible to obtain a QBO with a realistic period and to which both types of waves contribute. This is the regime in which the terrestrial QBO appears to reside. There may also be constraints on the initial strength of the wind shear, and these are similar to the constraints that apply when gravity wave drag is used without any planetary wave drag. In recent years, it has been observed that, in order to simulate the QBO accurately, general circulation models require parameterized gravity wave drag, in addition to the drag from resolved planetary-scale waves, and that even if the planetary wave amplitudes are incorrect, the gravity wave drag can be adjusted to compensate. This study provides a basis for knowing that such a compensation is possible. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/JAS3617.1
  10. Constraints on Wave Drag Parameterization Schemes for Simulating the Quasi-Biennial Oscillation. Part I: Gravity Wave Forcing Authors: Lucy J. Campbell and Theodore G. Shepherd Published: 1st December, 2005 Abstract: Parameterization schemes for the drag due to atmospheric gravity waves are discussed and compared in the context of a simple one-dimensional model of the quasi-biennial oscillation (QBO). A number of fundamental issues are examined in detail, with the goal of providing a better understanding of the mechanism by which gravity wave drag can produce an equatorial zonal wind oscillation. The gravity wave–driven QBOs are compared with those obtained from a parameterization of equatorial planetary waves. In all gravity wave cases, it is seen that the inclusion of vertical diffusion is crucial for the descent of the shear zones and the development of the QBO. An important difference between the schemes for the two types of waves is that in the case of equatorial planetary waves, vertical diffusion is needed only at the lowest levels, while for the gravity wave drag schemes it must be included at all levels. The question of whether there is downward propagation of influence in the simulated QBOs is addressed. In the gravity wave drag schemes, the evolution of the wind at a given level depends on the wind above, as well as on the wind below. This is in contrast to the parameterization for the equatorial planetary waves in which there is downward propagation of phase only. The stability of a zero-wind initial state is examined, and it is determined that a small perturbation to such a state will amplify with time to the extent that a zonal wind oscillation is permitted. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/JAS3616.1 I would like to thank Tom @Isotherm for recommending this paper.
  11. Observed and Simulated Teleconnections Between the Stratospheric Quasi‐Biennial Oscillation and Northern Hemisphere Winter Atmospheric Circulation Authors: Martin B. Andrews , Jeff R. Knight, Adam A. Scaife, Yixiong Lu, Tongwen Wu, Lesley J. Gray and Verena Schenzinger Published: 15th January, 2019 Abstract: The Quasi‐Biennial Oscillation (QBO) is the dominant mode of interannual variability in the tropical stratosphere, with easterly and westerly zonal wind regimes alternating over a period of about 28 months. It appears to influence the Northern Hemisphere winter stratospheric polar vortex and atmospheric circulation near the Earth's surface. However, the short observational record makes unequivocal identification of these surface connections challenging. To overcome this, we use a multicentury control simulation of a climate model with a realistic, spontaneously generated QBO to examine teleconnections with extratropical winter surface pressure patterns. Using a 30‐hPa index of the QBO, we demonstrate that the observed teleconnection with the Arctic Oscillation (AO) is likely to be real, and a teleconnection with the North Atlantic Oscillation (NAO) is probable, but not certain. Simulated QBO‐AO teleconnections are robust, but appear weaker than in observations. Despite this, inconsistency with the observational record cannot be formally demonstrated. To assess the robustness of our results, we use an alternative measure of the QBO, which selects QBO phases with westerly or easterly winds extending over a wider range of altitudes than phases selected by the single‐level index. We find increased strength and significance for both the AO and NAO responses, and better reproduction of the observed surface teleconnection patterns. Further, this QBO metric reveals that the simulated AO response is indeed likely to be weaker than observed. We conclude that the QBO can potentially provide another source of skill for Northern Hemisphere winter prediction, if its surface teleconnections can be accurately simulated. Link to full paper: https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2018JD029368
  12. Solar and QBO Influences on the Timing of Stratospheric Sudden Warmings Author: Lesley J. Gray Published: Dec 2004 Abstract: The interaction of the 11-yr solar cycle (SC) and the quasi-biennial oscillation (QBO) and their influence on the Northern Hemisphere (NH) polar vortex are studied using idealized model experiments and ECMWF Re-Analysis (ERA-40). In the model experiments, the sensitivity of the NH polar vortex to imposed easterlies at equatorial/subtropical latitudes over various height ranges is tested to explore the possible influence from zonal wind anomalies associated with the QBO and the 11-yr SC in those regions. The experiments show that the timing of the modeled stratospheric sudden warmings (SSWs) is sensitive to the imposed easterlies at the equator/subtropics. When easterlies are imposed in the equatorial or subtropical upper stratosphere, the onset of the SSWs is earlier. A mechanism is proposed in which zonal wind anomalies in the equatorial/subtropical upper stratosphere associated with the QBO and 11-yr SC either reinforce each other or cancel each other out. When they reinforce, as in Smin–QBO-east (Smin/E) and Smax–QBO-west (Smax/W), it is suggested that the resulting anomaly is large enough to influence the development of the Aleutian high and hence the time of onset of the SSWs. Although highly speculative, this mechanism may help to understand the puzzling observations that major warmings often occur in Smax/W years even though there is no strong waveguide provided by the QBO winds in the lower equatorial stratosphere. The ERA-40 data are used to investigate the QBO and solar signals and to determine whether the observations support the proposed mechanism. Composites of ERA-40 zonally averaged zonal winds based on the QBO (E/W), the SC (min/max), and both (Smin/E, Smin/W, Smax/E, Smax/W) are examined, with emphasis on the Northern Hemisphere winter vortex evolution. The major findings are that QBO/E years are more disturbed than QBO/W years, primarily during early winter. Sudden warmings in Smax years tend to occur later than in Smin years. Midwinter warmings are more likely during Smin/E and Smax/W years, although the latter result is only barely statistically significant at the 75% level. The data show some support for the proposed mechanism, but many more years are required before it can be fully tested. Link to full paper: https://journals.ametsoc.org/doi/10.1175/JAS-3297.1
  13. Stratospheric Control of the Madden–Julian Oscillation Author: Lesley J. Gray Published: Nov 2016 Abstract: Interannual variation of seasonal-mean tropical convection over the Indo-Pacific region is primarily controlled by El Niño–Southern Oscillation (ENSO). For example, during El Niño winters, seasonal-mean convection around the Maritime Continent becomes weaker than normal, while that over the central to eastern Pacific is strengthened. Similarly, subseasonal convective activity, which is associated with the Madden–Julian oscillation (MJO), is influenced by ENSO. The MJO activity tends to extend farther eastward to the date line during El Niño winters and contract toward the western Pacific during La Niña winters. However, the overall level of MJO activity across the Maritime Continent does not change much in response to the ENSO. It is shown that the boreal winter MJO amplitude is closely linked with the stratospheric quasi-biennial oscillation (QBO) rather than with ENSO. The MJO activity around the Maritime Continent becomes stronger and more organized during the easterly QBO winters. The QBO-related MJO change explains up to 40% of interannual variation of the boreal winter MJO amplitude. This result suggests that variability of the MJO and the related tropical–extratropical teleconnections can be better understood and predicted by taking not only the tropospheric circulation but also the stratospheric mean state into account. The seasonality of the QBO–MJO link and the possible mechanism are also discussed. Link to full paper: https://journals.ametsoc.org/doi/10.1175/JCLI-D-16-0620.1
  14. Sunspots, the QBO and the stratosphere in the North Polar Region – 20 years later Authors: Labitzke, Karin; Kunze, Markus; Brönnimann, Stefan Published: June 2006 Abstract: We have shown in earlier studies the size of the changes in the lower stratosphere which can be attributed to the 11-year sunspot cycle (SSC). We showed further that in order to detect the solar signal it is necessary to group the data according to the phase of the Quasi-Biennial Oscillation (QBO). Although this is valid throughout the year it was always obvious that the effect of the SSC and the QBO on the stratosphere was largest during the northern winters (January/February). Here we extend our first study (LABITZKE, 1987) by using additional data. Instead of 30 years of data, we now have 65 years. Results for the entire data set fully confirm the early findings and suggest a significant effect of the SSC on the strength of the stratospheric polar vortex and the mean meridional circulation. Link to full paper: (Paywall version) https://www.ingentaconnect.com/content/schweiz/mz/2006/00000015/00000003/art00013 Free-to-view copy: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.393.7345&rep=rep1&type=pdf
  15. Life cycle of the QBO-modulated 11-year solar cycle signals in the Northern Hemispheric winter Authors: Hua Lu, LesleyJ.Gray, Mark P. Baldwin and Martin J. Jarvis Published: April 2009 Abstract: This paper provides some insights on the quasi-biennial oscillation (QBO) modulated 11-year solar cycle (11-yr SC) signals in Northern Hemisphere (NH) winter temperature and zonal wind. Daily ERA-40 Reanalysis and ECMWF Operational data for the period of 1958 – 2006 were used to examine the seasonal evolution of the QBO-solar cycle relationship at various pressure levels up to the stratopause. The results show that the solar signals in the NH winter extratropics are indeed QBO-phase dependent, moving poleward and downward as winter progresses with a faster descent rate under westerly QBO than under easterly QBO. In the stratosphere, the signals are highly significant in late January to early March and have a life span of ∼30 – 50 days. Under westerly QBO, the stratospheric solar signals clearly lead and connect to those in the troposphere in late March and early April where they have a life span of ∼10 days. As the structure changes considerably from the upper stratosphere to the lower troposphere, the exact month when the maximum solar signals occur depends largely on the altitude chosen. For the low-latitude stratosphere, our analysis supports a vertical double-peaked structure of positive signature of the 11-yr SC in temperature, and demonstrates that this structure is further modulated by the QBO. These solar signals have a longer life span (∼3 – 4 months) in comparison to those in the extratropics. The solar signals in the lower stratosphere are stronger in early winter but weaker in late winter, while the reverse holds in the upper stratosphere. Link to full paper: https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/qj.419
  16. Interannual Modulation of Northern Hemisphere Winter Storm Tracks by the QBO Authors: Jiabao Wang, Hye‐Mi Kim, Edmund K. M. Chang Published: March 2018 Abstract: Storm tracks, defined as the preferred regions of extratropical synoptic‐scale disturbances, have remarkable impacts on global weather and climate systems. Causes of interannual storm track variation have been investigated mostly from a troposphere perspective. As shown in this study, Northern Hemisphere winter storm tracks are significantly modulated by the tropical stratosphere through the quasi‐biennial oscillation (QBO). The North Pacific storm track shifts poleward during the easterly QBO winters associated with a dipole change in the eddy refraction and baroclinicity. The North Atlantic storm track varies vertically with a downward shrinking (upward expansion) in easterly (westerly) QBO winters associated with the change of the tropopause height. These results not only fill the knowledge gap of QBO‐storm track relationship but also suggest a potential route to improve the seasonal prediction of extratropical storm activities owing to the high predictability of the QBO. Link to full paper: (Currently behind paywall) https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL076929
  17. Surface impacts of the Quasi Biennial Oscillation Authors: Lesley J. Gray, James A. Anstey, Yoshio Kawatani, Hua Lu, Scott Osprey, and Verena Schenzinger Published: June 2018 Abstract: Teleconnections between the Quasi Biennial Oscillation (QBO) and the Northern Hemisphere zonally averaged zonal winds, mean sea level pressure (mslp) and tropical precipitation are explored. The standard approach that defines the QBO using the equatorial zonal winds at a single pressure level is compared with the empirical orthogonal function approach that characterizes the vertical profile of the equatorial winds. Results are interpreted in terms of three potential routes of influence, referred to as the tropical, subtropical and polar routes. A novel technique is introduced to separate responses via the polar route that are associated with the stratospheric polar vortex, from the other two routes. A previously reported mslp response in January, with a pattern that resembles the positive phase of the North Atlantic Oscillation under QBO westerly conditions, is confirmed and found to be primarily associated with a QBO modulation of the stratospheric polar vortex. This mid-winter response is relatively insensitive to the exact height of the maximum QBO westerlies and a maximum positive response occurs with westerlies over a relatively deep range between 10 and 70 hPa. Two additional mslp responses are reported, in early winter (December) and late winter (February/March). In contrast to the January response the early and late winter responses show maximum sensitivity to the QBO winds at ∼20 and ∼70 hPa respectively, but are relatively insensitive to the QBO winds in between (∼50 hPa). The late winter response is centred over the North Pacific and is associated with QBO influence from the lowermost stratosphere at tropical/subtropical latitudes in the Pacific sector. The early winter response consists of anomalies over both the North Pacific and Europe, but the mechanism for this response is unclear. Increased precipitation occurs over the tropical western Pacific under westerly QBO conditions, particularly during boreal summer, with maximum sensitivity to the QBO winds at 70 hPa. The band of precipitation across the Pacific associated with the Inter-tropical Convergence Zone (ITCZ) shifts southward under QBO westerly conditions. The empirical orthogonal function (EOF)-based analysis suggests that this ITCZ precipitation response may be particularly sensitive to the vertical wind shear in the vicinity of 70 hPa and hence the tropical tropopause temperatures. Link to full paper: https://www.atmos-chem-phys.net/18/8227/2018/acp-18-8227-2018.pdf
  18. Tropospheric QBO–ENSO Interactions and Differences between the Atlantic and Pacific Authors: Felicitas Hansen GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany Katja Matthes GEOMAR Helmholtz Centre for Ocean Research Kiel, and Christian-Albrechts-Universität zu Kiel, Kiel, Germany Sebastian Wahl GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany Date: 20th November 2015 Abstract: This study investigates the interaction of the quasi-biennial oscillation (QBO) and the El Niño–Southern Oscillation (ENSO) in the troposphere separately for the North Pacific and North Atlantic region. Three 145-yr model simulations with NCAR’s Community Earth System Model Whole Atmosphere Community Climate Model (CESM-WACCM) are analyzed where only natural (no anthropogenic) forcings are considered. These long simulations allow the authors to obtain statistically reliable results from an exceptional large number of cases for each combination of the QBO (westerly and easterly) and ENSO phases (El Niño and La Niña). Two different analysis methods were applied to investigate where nonlinearity might play a role in QBO–ENSO interactions. The analyses reveal that the stratospheric equatorial QBO anomalies extend down to the troposphere over the North Pacific during Northern Hemisphere winter only during La Niña and not during El Niño events. The Aleutian low is deepened during QBO westerly (QBOW) as compared to QBO easterly (QBOE) conditions, and the North Pacific subtropical jet is shifted northward during La Niña. In the North Atlantic, the interaction of QBOW with La Niña conditions (QBOE with El Niño) results in a positive (negative) North Atlantic Oscillation (NAO) pattern. For both regions, nonlinear interactions between the QBO and ENSO might play a role. The results provide the potential to enhance the skill of tropospheric seasonal predictions in the North Atlantic and North Pacific region. Link to original text: https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-15-0164.1?download=true
  19. Extratropical Atmospheric Predictability From the Quasi-Biennial Oscillation in Subseasonal Forecast Models Authors: Chaim I. Garfinkel, Chen Schwartz, Daniela I. V. Domeisen, Seok-Woo Son, Amy H. Butler, Ian P. White. Published: July 2018 Abstract: The effect of the Quasi-Biennial Oscillation (QBO) on the Northern Hemisphere wintertime stratospheric polar vortex is evaluated in five operational subseasonal forecasting models. Of these five models, the three with the best stratospheric resolution all indicate a weakened vortex during the easterly phase of the QBO relative to its westerly phase, consistent with the Holton-Tan effect. The magnitude of this effect is well captured for initializations in late October and November in the model with the largest ensemble size. While the QBO appears to modulate the extratropical tropospheric circulation in some of the models as well, the importance of a polar stratospheric pathway, through the Holton-Tan effect, for the tropospheric anomalies is unclear. Overall, knowledge of the QBO can contribute to enhanced predictability, at least in a probabilistic sense, of the Northern Hemisphere winter climate on subseasonal timescales. Plain Language Summary The Quasi-Biennial Oscillation (QBO) is perhaps the most regular atmospheric phenomena that is not directly controlled by solar radiation and can be predicted more than a year in advance. It is characterized by alternating westerly and easterly winds in the tropical stratosphere. Here we show that the QBO can be used to improve month-ahead prediction of the Northern Hemisphere wintertime stratospheric polar vortex, and perhaps even the extratropical tropospheric circulation. Link to full paper: https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2018JD028724
  20. Dynamics of the Disrupted 2015/16 Quasi-Biennial Oscillation Author: Lawrence Coy, NASA Goddard Space Flight Center, Greenbelt, and Science Systems and Applications, Inc., Lanham, Maryland. Published: June 2017 Abstract: A significant disruption of the quasi-biennial oscillation (QBO) occurred during the Northern Hemisphere (NH) winter of 2015/16. Since the QBO is the major wind variability source in the tropical lower stratosphere and influences the rate of ascent of air entering the stratosphere, understanding the cause of this singular disruption may provide new insights into the variability and sensitivity of the global climate system. Here this disruptive event is examined using global reanalysis winds and temperatures from 1980 to 2016. Results reveal record maxima in tropical horizontal momentum fluxes and wave forcing of the tropical zonal mean zonal wind over the NH 2015/16 winter. The Rossby waves responsible for these record tropical values appear to originate in the NH and were focused strongly into the tropics at the 40-hPa level. Two additional NH winters, 1987/88 and 2010/11, were also found to have large tropical lower-stratospheric momentum flux divergences; however, the QBO westerlies did not change to easterlies in those cases. Link to full paper: https://journals.ametsoc.org/doi/10.1175/JCLI-D-16-0663.1
  21. Kelvin Waves - A Learner's Guide Authors: B Wang, University of Hawaii, Honolulu, HI, USA Published: Encylopedia of Atmospheric Scieinces, 2002 Introduction: The Kelvin wave is a large-scale wave motion of great practical importance in the Earth’s atmosphere and ocean. Discovered by Sir William Thompson (who later became Lord Kelvin) in 1879, the Kelvin wave is a special type of gravity wave that is affected by the Earth’s rotation and trapped at the Equator or along lateral vertical boundaries such as coastlines or mountain ranges. The existence of the Kelvin wave relies on (a) gravity and stable stratification for sustaining a gravitational oscillation, (b) significant Coriolis acceleration, and (c) the presence of vertical boundaries or the equator. The unique feature of the Kelvin wave is its unidirectional propagation. The Kelvin wave moves equatorward along a western boundary, poleward along an eastern boundary, and cyclonically around a closed boundary (counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere). The wave amplitude is largest at the boundary and decays exponentially with distance from it. At the Equator, Kelvin waves always propagate eastward, reaching their maximum magnitude at the Equator and decaying exponentially with increasing latitude. There are two basic types of Kelvin waves: boundary trapped and equatorially trapped. Each type of Kelvin wave may be further subdivided into surface and internal Kelvin waves. Surface, or barotropic, waves penetrate the entire depth of the fluid. Kelvin waves also appear within the stably stratified ocean and atmosphere, and are called internal, or baroclinic, Kelvin waves. Internal Kelvin waves are often found in a layer with large density gradients; the density gradient acts as an interface that allows the existence of internal gravity waves. Examples of such density gradients are the oceanic thermocline (a layer of large vertical temperature gradient separating a shallow layer of warm surface water about 50–200 m deep and a much deeper layer of cold water below) and the lower edge of an atmospheric inversion, a layer in which temperature increases with height. Like gravity waves, Kelvin waves can also propagate vertically in a continuously stratified geophysical fluid. Atmospheric Kelvin waves play an important role in the adjustment of the tropical atmosphere to convective latent heat release, in the stratospheric quasibiennial oscillation, and in the generation and maintenance of the Madden–Julian Oscillation. Oceanic Kelvin waves play a critical role in tidal motion, in the adjustment of the tropical ocean to wind stress forcing, and in generating and sustaining the El Nin˜o Southern Oscillation. Link to full paper: https://www.soest.hawaii.edu/MET/Faculty/bwang/bw/paper/wang_103.pdf
  22. Nonlinearity of the combined warm ENSO and QBO effects on the Northern Hemisphere polar vortex in MAECHAM5 simulations Authors: Natalia Calvo, Marco A. Giorgetta, Ricardo Garcia‐Herrera and Elisa Manzini Published: 14th July, 2009 Abstract: The influence of the quasi‐biennial oscillation (QBO) on the Northern Hemisphere (NH) polar vortex response to warm El Niño–Southern Oscillation (ENSO) events and the impact of the warm ENSO events on the QBO signal in the NH polar stratosphere have been analyzed using the Middle Atmosphere ECHAM5 model. The experiment setup was designed to include simulations of extended NH winter seasons for either strong easterly or strong westerly phases of the tropical QBO, forced with either sea surface temperatures (SSTs) from the strong ENSO event that occurred in 1997/1998 or with climatological SSTs. It has been found that the weakening and warming of the polar vortex associated with a warm ENSO are intensified at the end of the winter during both QBO phases. In addition, the westerly QBO phase delays the onset of the warm ENSO signal, while the easterly QBO phase advances it. Warm ENSO events also impact the extratropical signal of the QBO by intensifying (weakening) the QBO effects in early (late) winter. Therefore, it appears that during warm ENSO events the duration of QBO signal in the northern extratropics is shortened while its downward propagation accelerated. Our dynamical analysis has revealed that these results are due to changes in the background flow caused by the QBO combined with changes in the anomalous propagation and dissipation of extratropical waves generated by warm ENSO. In both cases, a nonlinear behavior in the response of the polar vortex is observed when both warm ENSO and the easterly phase of the QBO operate together. These results suggest that the Arctic polar vortex response to combined forcing factors, in our case warm ENSO and the QBO phenomena, is expected to be nonlinear also for other coexistent forcing factors able to affect the variability of the vortex in the stratosphere. Link to full paper: https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2008JD011445
  23. Relationship Between Phase of the Quasi-Biennial Oscillation (QBO) and MJO Propagation Through the Maritime Continent - Presentation A presentation at the AMS 33rd Conference on “Hurricanes and Tropical Meteorology” held at Ponte Vedra, Florida, USA between 16th and 20th April, 2018 Presenters: Casey R Densmore, B. S. Barrett, E. R. Sanabia and P. Ray Presentation Date: 18th April, 2018 Presentation Summary: One region particularly favorable for enhanced convective activity during the Madden Julian Oscillation (MJO) active phase is the Maritime Continent (MC). As the ascending branch of the MJO envelope reaches the MC, it sometimes propagates eastward and reaches the Western Pacific Ocean (a propagating event). However, the convective envelope may also decouple from zonal wind anomalies and weaken over the MC, not reaching the Western Pacific Ocean (a non-propagating event). Propagation of the MJO across the MC is currently an active area of research. In this study, anomalies of specific humidity, lower and upper tropospheric zonal (u) and meridional (v) wind components, geopotential height, and temperature from the European Centre for Long-Range Weather Forecasts (ECMWF) ERA-Interim Reanalysis were compared for propagating and non-propagating MJO events. Equatorial zonal wind anomalies over the Maritime Continent at 50 hPa were used to define QBO phase. The Wheeler-Hendon Realtime Multivariate (RMM) MJO Index was used to classify and categorize the geographic location (e.g. phase) and intensity (e.g. amplitude). Of particular emphases were differences in the mean atmospheric states for easterly, westerly, and neutral QBO phases for different MJO propagating events. The goal of this work was to better understand the physical mechanisms that favor MJO propagation across the MC. Link to conference video presentation (15 minutes): https://ams.confex.com/ams/33HURRICANE/videogateway.cgi/id/46828?recordingid=46828&uniqueid=Paper339768&entry_password=942250 Link to full conference agenda: https://ams.confex.com/ams/33HURRICANE/webprogram/33HURRICANE.html
  24. Modulation of the Northern Hemisphere Midlatitude Flow and Extreme Events By the Madden-Julian Oscillation - Presentation A presentation at the AMS 33rd Conference on “Hurricanes and Tropical Meteorology” held at Ponte Vedra, Florida, USA between 16th and 20th April, 2018 Presenters: Eric D. Maloney, E. A. Barnes, C. F. Baggett, K. C. Tseng, B. D. Mundhenk, S. Henderson and B. Wolding Presentation Date: 16th April, 2018 Presentation Summary: Recent work on teleconnections between the Madden-Julian oscillation (MJO) and northern Hemisphere midlatitude geopotential height anomalies, blocking, and atmospheric rivers (ARs) are discussed. It is first demonstrated using reanalysis fields and a linear baroclinic model that MJO teleconnections to higher latitudes are more robust during certain MJO phases due to the spatial configuration of MJO heating anomalies relative to the North Pacific jet. This robustness is also reflected in excellent ensemble agreement in prediction of North Pacific geopotential height anomalies in a leading numerical weather prediction model at 3-week lead times for certain MJO phases. It is demonstrated that climate and weather forecasting models can have difficulty simulating the spatial pattern and strength of such teleconnections not only due to poor MJO performance, but also due to biases in the spatial extent of the North Pacific jet that affect the pathway of Rossby wave propagation into high latitudes. The modulation of atmospheric blocking and atmospheric river (AR) activity associated with these MJO teleconnections are discussed. It is also shown that the nature of the MJO teleconnection to the Northern Hemisphere depends on the phase of the tropical quasi-biennial oscillation (QBO). The QBO phase-dependent modulation of AR activity by the MJO along the west coast of North America area is presented. A statistical prediction scheme for anomalous AR activity using the initial state of the MJO and QBO as the sole predictors is developed. When evaluated over 36 boreal winters, it is found that certain combinations of MJO and QBO phases produce predictive skill for anomalous AR activity up to 5 weeks in advance that exceeds that produced by a state-of-the-art numerical weather prediction model. Finally, recent modeling results suggest that the MJO teleconnection to higher latitudes may weaken in a warmer climate. The implications of these weaker teleconnections for subseasonal prediction of blocking and ARs will be discussed. Link to conference video presentation (15 minutes): https://ams.confex.com/ams/33HURRICANE/videogateway.cgi/id/46438?recordingid=46438&uniqueid=Paper339784&entry_password=812548 Link to full conference agenda: https://ams.confex.com/ams/33HURRICANE/webprogram/33HURRICANE.html
  25. Effects of stratospheric variability on El Niño teleconnections Authors: J H Richter, C Deser and L Sun Published: 17th December, 2015 Abstract: The effects of the tropical Pacific El Niño Southern Oscillation (ENSO) phenomenon are communicated to the rest of the globe via atmospheric teleconnections. Traditionally, ENSO teleconnections have been viewed as tropospheric phenomena, propagating to higher latitudes as Rossby waves. Recent studies, however, suggest an influence of the stratosphere on extra-tropical ENSO teleconnections. The stratosphere is highly variable: in the tropics, the primary mode of variability is the quasi-biennial oscillation (QBO), and in the extra-tropics sudden stratospheric warmings (SSWs) regularly perturb the mean state. Here, we conduct a 10-member ensemble of simulations with a stratosphere-resolving atmospheric general circulation model forced with the observed evolution of sea surface temperatures during 1952–2001 to examine the effects of the QBO and SSWs on the zonal-mean circulation and temperature response to El Niño, with a focus on the northern extra-tropics during winter. We find that SSWs have a larger impact than the QBO on the composite El Niño responses. During El Niño winters with SSWs, the polar stratosphere shows positive temperature anomalies that propagate downward to the surface where they are associated with increased sea-level pressure over the Arctic. During El Niño winters without SSWs, the stratosphere and upper troposphere show negative temperature anomalies but these do not reach the surface. The QBO modulates the El Niño teleconnection primarily in winters without SSWs: the negative temperature anomalies in the polar stratosphere and upper troposphere are twice as large during QBO West compared to QBO East years. In addition, El Niño winters that coincide with the QBO West phase show stronger positive sea-level pressure anomalies over the eastern Atlantic and Northern Europe than those in the QBO East phase. The results imply that the stratosphere imparts considerable variability to ENSO teleconnections. Link to full paper: http://iopscience.iop.org/article/10.1088/1748-9326/10/12/124021
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