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  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. Features Total AAM, Bias Corrected Rel AAM GEFS, CFS GWO Forecast. He stated he is soon to add torque products. Nick Schraldi GWO Site Non-Bias Corrected GEFS GWO forecast. Michael Ventrice Hovmoller from MV, to help spot AAM trends and patterns. GEFS. Carl Schreck More Hovmollers and other tropical charts to spot trends in the AAM. CFS forecast. NPJ Phase Diagrams/Albany Shows a GEFS forecast and observation of NP jetstream, which is largely controlled by the AAM. From @Bring Back 1962-63: Since the service provided through WDT was withdrawn there was a gap in this vitally important data. I've been in touch with Ed Berry, who along with Dr Klaus Weickmann (who retired 2 years ago) developed the GSDM (I posted on that on both the 33 and NetWx forums with Ed's excellent presentation earlier this year) and he told me that a friend of his still processes this data. He has kindly provided a link to that site plus the access user name and password: un = gsdm01 pw = gu3st#1 That will take you to this page where you'll find a lot more than just the ex WDT data: Monitoring of Global Atmospheric Angular Momentum (AAM) Budget NCEP-NCAR Reanalysis DAILY DATA Vertically-integrated 5-day running mean: 1968-1997 Climatology Plots show some of the features: MJO, SUB-MONTHLY, & RAPID TRANSITIONS. ( Plots contain data through (MM/DD/YYYY) = 09/26/2018 ) PLOTS LATEST 90 DAYS LATEST 90 DAYS w/ Seasonal Cycle CURRENT YEAR CURRENT YEAR w/ Seasonal Cycle Data Files AAM data file (Updated: Friday, 28-Sep-2018 08:35:48 CDT) AAM 1-21 data file (Updated: Friday, 28-Sep-2018 08:35:50 CDT) TAUC data file (Updated: Friday, 28-Sep-2018 08:35:57 CDT) TAUF data file (Updated: Friday, 28-Sep-2018 08:35:57 CDT) TAUG data file (Updated: Friday, 28-Sep-2018 08:35:57 CDT) TAUM data file (Updated: Friday, 28-Sep-2018 08:35:57 CDT) TEND data file (Updated: Friday, 28-Sep-2018 08:36:00 CDT) TEND (1-21) data file (Updated: Friday, 28-Sep-2018 08:36:02 CDT) TRANSP data file (Updated: Friday, 28-Sep-2018 08:36:00 CDT) MONTHLY DATA Vertically-integrated: 1968-1997 Climatology Plots show some of the features: ENSO, QBO, & TRENDS. ( Plots contain data through 08/31/2018 ) PLOTS 1958-PRESENT: Total Fields 1958-PRESENT: Anomaly Fields MJO Composites:
  2. 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:
  3. 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:
  4. 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:
  5. 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) Free-to-view copy:
  6. 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:
  7. 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)
  8. 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:
  9. 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:
  10. 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:
  11. 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:
  12. 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:
  13. 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:
  14. 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): Link to full conference agenda:
  15. 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): Link to full conference agenda:
  16. 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:
  17. Parameterized Gravity Wave Momentum Fluxes from Sources Related to Convection and Large-Scale Precipitation Processes in a Global Atmosphere Model Authors: Andrew C. Bushell Published: 31st July, 2015 Abstract: Analysis of a high-resolution, convection-permitting simulation of the tropical Indian Ocean has revealed empirical relationships between precipitation and gravity wave vertical momentum flux on grid scales typical of earth system models. Hence, the authors take a rough functional form, whereby the wave flux source spectrum has an amplitude proportional to the square root of total precipitation, to represent gravity wave source strengths in the Met Office global model’s spectral nonorographic scheme. Key advantages of the new source are simplicity and responsiveness to changes in convection processes without dependence upon model-specific details of their representation. Thus, the new source scheme is potentially a straightforward adaptation for a class of spectral gravity wave schemes widely used for current state-of-the-art earth system models. Against an invariant source, the new parameterized source generates launch-level flux amplitudes with greater spatial and temporal variability, producing probability density functions for absolute momentum flux over the ocean that have extended tails of large-amplitude, low-occurrence events. Such distributions appear more realistic in comparison with reported balloon observations. Source intermittency at the launch level affects mean fluxes at higher levels in two ways: directly, as a result of upward propagation of the new source variation, and indirectly, through changes in filtering characteristics that arise from intermittency. Initial assessment of the new scheme in the Met Office global model indicates an improved representation of the quasi-biennial oscillation and sensitivity that offers potential for further impact in the future. Link to full paper:
  18. Regional Variations in Gravity Waves, Latent Heating, and the Tropical Circulation Authors: M. Joan Alexander Presentation Date: 24th July, 2017 Presentation Summary: Convective latent heating is an efficient generator of atmospheric gravity waves. Convectively generated gravity waves emanating from rain storms are observed far from their sources and at all levels in the atmosphere: At the surface, in the stratosphere, and even beyond in the mesosphere and thermosphere. They are common in the tropics, but are also observed at mid-latitudes and in all seasons. Convectively generated gravity waves transport momentum and drive remote changes in the circulation where they dissipate, and through this process they link fine-scale precipitation events to mesoscale and global-scale circulation changes. At tropical latitudes, convectively generated gravity waves occur on a particularly broad range of scales and frequencies. Collectively the full spectrum of gravity waves drives the quasi-biennial oscillation (QBO) in lower stratospheric zonal-mean winds. The key characteristics of the QBO are zonal mean winds that oscillate from easterly to westerly with an average period of 28 months. The circulation is not locked to the annual cycle, but rather the period is inversely related to atmospheric wave momentum transport, or more specifically to the wave momentum forcing. The QBO has known influences on seasonal predictability, but global seasonal prediction models still severely under-resolve gravity waves and their effects on the circulation. Observations show a links between the phase of the El Nino Southern Oscillation (ENSO) and the period and amplitude of the QBO. Additional observational evidence suggests a causal link between the phase of the QBO and modulation in the strength of intraseasonal precipitation variability in the Madden-Julian Oscillation (MJO). Global characterizations of gravity waves and their momentum transport remain an observational challenge due to their small scales, high frequencies, and intermittent occurrences. Idealized models therefore play a major role in our understanding of tropical gravity waves and their effects on circulation. We present results of idealized model simulations of realistic gravity waves generated by observed precipitation and cloud variability. Regional changes in gravity wave generation and gravity wave drag and their relationships to ENSO and MJO precipitation and circulation patterns are examined. ENSO changes not only the regional pattern of tropical gravity wave sources, but also changes the wave propagation properties and wave effects on the stratospheric circulation. Gravity waves in the model occur in strong, localized, intermittent wave packets that break at lower altitudes than commonly assumed. Gravity wave occurrences above convection near the tropopause are not only tied to regional variations in precipitation, but also show a strong dependence on regional tropopause wind patterns. Our idealized model studies of waves generated by tropical convection show how global-scale waves affect the regional patterns in gravity wave occurrence and affect the net upward flux of zonal momentum into the stratosphere. Link to full paper: Not available as behind the AGU100 paywall but there video presentation at the AMS 17th Conference on "Mesoscale Processes" held at Coral Reef Harbor, Crowne Plaza, San Diego between 24th and 27th July, 2017. Link to conference video presentation :
  19. Varying stratospheric responses to tropical Atlantic SST forcing from early to late winter Authors: Jian Rao and Rongcai Ren Published: 9th November, 2017 Abstract: Using multiple reanalysis datasets and model simulations, we begin in this study by isolating the tropical Atlantic Ocean (TAO) sea surface temperature (SST) signals that are independent from ENSO, and then investigate their influences on the northern winter stratosphere. It is revealed that TAO SST forcing does indeed have significant effects on the northern winter stratosphere, but these effects vary from early to late winter in a way that explains the overall insignificant effect when the seasonal average is considered. The stratospheric polar vortex is anomalously weaker/warmer in November–December, stronger/colder in January–March, and weaker/warmer again in April–May during warm TAO years. The varying impacts of the TAO forcing on the extratropical stratosphere are related to a three-stage response of the extratropical troposphere to the TAO forcing during cold season. The tropospheric circulation exhibits a negative North Atlantic Oscillation–like response during early winter, an eastward propagating Rossby wave pattern in mid-to-late winter, and a meridional dipole over North America in spring. Associated with this is varying planetary wave activity in the stratosphere, manifested as an increase in early winter, a decrease in mid-to-late winter, and an increase again in spring. The varying modulation of stratospheric circulation by TAO forcing is consistently confirmed in three reanalysis datasets, and model simulations (fully coupled model and its component AGCM). The exception to the robustness of this verification is that the circumpolar wind response in the fully coupled model is relatively weaker, and that in its component AGCM appears a month later than observed. Link to full paper:
  20. Snow–(N)AO Teleconnection and Its Modulation by the Quasi-Biennial Oscillation Authors: Y. Peings Published: 29th November, 2017 Abstract: This study explores the wintertime extratropical atmospheric response to Siberian snow anomalies in fall, using observations and two distinct atmospheric general circulation models. The role of the quasi-biennial oscillation (QBO) in modulating this response is discussed by differentiating easterly and westerly QBO years. The remote influence of Siberian snow anomalies is found to be weak in the models, especially in the stratosphere where the “Holton–Tan” effect of the QBO dominates the simulated snow influence on the polar vortex. At the surface, discrepancies between composite analyses from observations and model results question the causal relationship between snow and the atmospheric circulation, suggesting that the atmosphere might have driven snow anomalies rather than the other way around. When both forcings are combined, the simulations suggest destructive interference between the response to positive snow anomalies and easterly QBO (and vice versa), at odds with the hypothesis that the snow–North Atlantic Oscillation/Arctic Oscillation [(N)AO] teleconnection in recent decades has been promoted by the QBO. Although model limitations in capturing the relationship exist, altogether these results suggest that the snow–(N)AO teleconnection may be a stochastic artifact rather than a genuine atmospheric response to snow-cover variability. This study adds to a growing body of evidence suggesting that climate models do not capture a robust and stationary snow–(N)AO relationship. It also highlights the need for extending observations and/or improving models to progress on this matter. Link to full paper:
  21. Interannual variability in the gravity wave drag – vertical coupling and possible climate links Authors: Petr Šácha, Jiri Miksovsky and Petr Pisoft Published: 24th May, 2018 Abstract: Gravity wave drag (GWD) is an important driver of the middle atmospheric dynamics. However, there are almost no observational constraints on its strength and distribution (especially horizontal). In this study we analyze orographic GWD (OGWD) output from Canadian Middle Atmosphere Model simulation with specified dynamics (CMAM-sd) to illustrate the interannual variability in the OGWD distribution at particular pressure levels in the stratosphere and its relation to major climate oscillations. We have found significant changes in the OGWD distribution and strength depending on the phase of the North Atlantic Oscillation (NAO), quasi-biennial oscillation (QBO) and El Niño–Southern Oscillation. The OGWD variability is shown to be induced by lower-tropospheric wind variations to a large extent, and there is also significant variability detected in near-surface momentum fluxes. We argue that the orographic gravity waves (OGWs) and gravity waves (GWs) in general can be a quick mediator of the tropospheric variability into the stratosphere as the modifications of the OGWD distribution can result in different impacts on the stratospheric dynamics during different phases of the studied climate oscillations. Link to full paper: Link to the Supplement:
  22. Different ENSO teleconnections and their effects on the stratospheric polar vortex Authors: C. I. Garfinkel and D. L. Hartmann Published: 30th September, 2008 Abstract: Reanalysis data are used to study the El Niño–Southern Oscillation (ENSO) signal in the troposphere and stratosphere during the late fall to midwinter period. Warm ENSO events have extratropical tropospheric teleconnections that increase the wave 1 eddies and reduce the wave 2 eddies, as compared to cold ENSO. The increase in wave 1 overwhelms the decrease in wave 2, so the net effect is a weakened vortex. This modification in tropospheric wave forcing is induced by a deepening of the wintertime Aleutian low via the Pacific–North America pattern (PNA). Model results are also used to verify that the PNA is the primary mechanism through which ENSO modulates the vortex. During easterly Quasi‐Biennial Oscillation (EQBO), warm ENSO does not show a PNA response in the observational record. Consequently, the polar vortex does not show a strong response to the different phases of ENSO under EQBO, nor to the different phases of QBO under WENSO. It is not clear whether the lack of a PNA response to warm ENSO during EQBO is a real physical phenomenon or a feature of the limited data record we have. Link to full paper:
  23. The Influence of the Solar Cycle and QBO on the Late-Winter Stratospheric Polar Vortex Authers: Camp, Tung. Published: July 2006 Abstract: Link to full paper:
  24. Northern Hemisphere mid‐winter vortex‐displacement and vortex‐split stratospheric sudden warmings: Influence of the Madden‐Julian Oscillation and Quasi‐Biennial Oscillation Authors: Chuanxi Liu, Baijun Tian, King-Fai Li, Gloria L. Manney, Nathaniel J. Livesey , Yuk L. Yung and Duane E. Waliser First Published: 13th October, 2014 Abstract: We investigate the connection between the equatorial Madden‐Julian Oscillation (MJO) and different types of the Northern Hemisphere mid‐winter major stratospheric sudden warmings (SSWs), i.e., vortex‐displacement and vortex‐split SSWs. The MJO‐SSW relationship for vortex‐split SSWs is stronger than that for vortex‐displacement SSWs, as a result of the stronger and more coherent eastward propagating MJOs before vortex‐split SSWs than those before vortex‐displacement SSWs. Composite analysis indicates that both the intensity and propagation features of MJO may influence the MJO‐related circulation pattern at high latitudes and the type of SSWs. A pronounced Quasi‐Biennial Oscillation (QBO) dependence is found for vortex‐displacement and vortex‐split SSWs, with vortex‐displacement (‐split) SSWs occurring preferentially in easterly (westerly) QBO phases. The lagged composites suggest that the MJO‐related anomalies in the Arctic are very likely initiated when the MJO‐related convection is active over the equatorial Indian Ocean (around the MJO phase 3). Further analysis suggests that the QBO may modulate the MJO‐related wave disturbances via its influence on the upper tropospheric subtropical jet. As a result, the MJO‐related circulation pattern in the Arctic tends to be wave number‐one/wave number‐two ~25–30 days following phase 3 (i.e., approximately phases 7–8, when the MJO‐related convection is active over the western Pacific) during easterly/westerly QBO phases, which resembles the circulation pattern associated with vortex‐displacement/vortex‐split SSWs. Link to Paper:
  25. Influences of the 11-year sunspot cycle on the stratosphere – and the importance of the QBO Lecture by: Karin Labitzke, Institute for Meteorology, F.U. Berlin Germany Presented at the International Workshop on the "Solar Variability, Earth’s Climate and the Space Environment" held at Bozeman, Montana Date: 1st to 6th June, 2008 Abstract (from the workshop programme - see 2nd link below): Large effects of solar variability related to the 11-year sunspot cycle are seen in the stratosphere, but only if the data are grouped according to the phase of the QBO. New results based on an extended, 66-year long data set fully confirm earlier findings and suggest a significant effect of the SSC on the occurrence of the Major Midwinter Warmings (MMWs) over the Arctic as well as on the strength of the stratospheric polar vortex and on the mean meridional circulation. The stratosphere is least disturbed during the northern summer when the interannual variability is small. And if the different phases of the QBO are introduced, a large solar signal is found. It is shown that the QBO not only modulates the solar signal on the decadal scale, but that the QBO is itself modulated by the solar variability Link to full paper: Link to full International Workshop programme (6 days):
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