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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. 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. From @Bring Back 1962-63: Since the service provided through WDT was withdrawn there was a gap in this vitally important data.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: http://gsdmsolutions.com/~gsdm/clim/aam.rean.shtml 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: http://www.atmos.albany.edu/facstaff/roundy/waves/rmmcyc/index200reg.html
  2. Response of the Zonal Mean Atmospheric Circulation to El Niño versus Global Warming Authors: Jian Lu, Gang Chen and Dargan M. W. Frierson First Published: March 11th, 2008 Published on line: November 15th, 2008 Abstract: The change in the zonal mean atmospheric circulation under global warming is studied in comparison with the response to El Niño forcing, by examining the model simulations conducted for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. In contrast to the strengthening and contraction of the Hadley cell and the equatorward shift of the tropospheric zonal jets in response to El Niño, the Hadley cell weakens and expands poleward, and the jets move poleward in a warmed climate, despite the projected “El Niño–like” enhanced warming over the equatorial central and eastern Pacific. The hydrological impacts of global warming also exhibit distinct patterns over the subtropics and midlatitudes in comparison to the El Niño. Two feasible mechanisms are proposed for the zonal mean circulation response to global warming: 1) The increase in static stability of the subtropical and midlatitude troposphere, a robust result of the quasi-moist adiabatic adjustment to the surface warming, may stabilize the baroclinic eddy growth on the equatorward side of the storm tracks and push the eddy activity and the associated eddy-driven wind and subsidence poleward, leading to the poleward expansion of the Hadley cell and the shift of midlatitude jets; 2) the strengthening of the midlatitude wind at the upper troposphere and lower stratosphere, arguably a consequence of increases in the meridional temperature gradient near the tropopause level due to the tropospheric warming and tropopause slope, may increase the eastward propagation of the eddies emanating from the midlatitudes, and thus the subtropical region of wave breaking displaces poleward together with the eddy-driven circulation. Both mechanisms are somewhat, if not completely, distinct from those in response to the El Niño condition. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/2008JCLI2200.1 Credit goes to Eric @Webberweather for finding this presentation - thank you.
  3. Relationship between Tropical Pacific SST and global atmospheric angular momentum in coupled models Authors: Huei−Ping Huang, Matthew Newman, Richard Seager, Yochanan Kushnir and Participating CMIP2+ Modeling Groups First Published: January 2004 Abstract: The sensitivity parameter S1 = ∆AAM/∆SST, where ∆AAM and ∆SST represent the anomalies of global atmospheric angular momentum (AAM) and tropical Pacific sea surface temperature (SST) in the NINO3.4 region, is compared for the CMIP2+ coupled models. The parameter quantifies the strength of atmospheric zonal mean zonal wind response to SST anomaly in the equatorial Pacific, an important process for the climate system. Although the simulated ∆AAM and ∆SST are found to exhibit great disparity, their ratios agree better among the coupled models (and with observation) with no significant outliers. This indicates that the processes that connect the AAM anomaly to tropical SST anomaly are not sensitive to the base SST and the detail of convective heating and are relatively easy to reproduce by the coupled models. Through this robust ∆SST−∆AAM relationship, the model bias in tropical Pacific SST manifests itself in the bias in atmospheric angular momentum. The value of S1 for an atmospheric model forced by observed SST is close to that for a coupled model with a similar atmospheric component, suggesting that the ∆SST− ∆AAM relationship is dominated by a one−way influence of the former forcing the latter. The physical basis for the ∆SST−∆AAM relationship is explored using a statistical equilibrium argument that links ∆SST to the anomaly of tropical tropospheric temperature. The resulting meridional gradient of tropospheric temperature is then linked to the change in zonal wind in the subtropical jets, the main contributor to ∆AAM, by thermal wind balance. Link to Paper: https://pcmdi.llnl.gov/mips/cmip/cmip_abstracts/huang04.pdf?id=95 Credit goes to Tom @Isotherm for finding this paper - thank you.
  4. Centennial Trend and Decadal-to-Interdecadal Variability of Atmospheric Angular Momentum in CMIP3 and CMIP5 Simulations Authors: Houk Paek and Huei-Ping Huang First Published: 26th November, 2012 Published on line: 31st May, 2013 Abstract: The climatology and trend of atmospheric angular momentum from the phase 3 and the phase 5 Climate Model Intercomparison Project (CMIP3 and CMIP5, respectively) simulations are diagnosed and validated with the Twentieth Century Reanalysis (20CR). It is found that CMIP5 models produced a significantly smaller bias in the twentieth-century climatology of the relative MR and omega MΩ angular momentum compared to CMIP3. The CMIP5 models also produced a narrower ensemble spread of the climatology and trend of MR and MΩ. Both CMIP3 and CMIP5 simulations consistently produced a positive trend in MR and MΩ for the twentieth and twenty-first centuries. The trend for the twenty-first century is much greater, reflecting the role of greenhouse gas (GHG) forcing in inducing the trend. The simulated increase in MR for the twentieth century is consistent with reanalysis. Both CMIP3 and CMIP5 models produced a wide range of magnitudes of decadal and interdecadal variability of MRcompared to 20CR. The ratio of the simulated standard deviation of decadal or interdecadal variability to its observed counterpart ranges from 0.5 to over 2.0 for individual models. Nevertheless, the bias is largely random and ensemble averaging brings the ratio to within 18% of the reanalysis for decadal and interdecadal variability for both CMIP3 and CMIP5. The twenty-first-century simulations from both CMIP3 and CMIP5 produced only a small trend in the amplitude of decadal or interdecadal variability, which is not statistically significant. Thus, while GHG forcing induces a significant increase in the climatological mean of angular momentum, it does not significantly affect its decadal-to-interdecadal variability in the twenty-first century. Link to Paper: https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-12-00515.1
  5. Unusual Behavior in Atmospheric Angular Momentum during the 1965 and 1972 El Niños Authors: Huei-Ping Huang, Klaus M. Weickmann and Richard D. Rosen First Published: 24th February, 2003 Published on line: 1st August, 2003 Abstract: The global atmospheric angular momentum (AAM) is known to increase with tropical eastern Pacific sea surface temperature (SST) anomalies during El Niño events. Using a reanalysis dataset, the ratio of the monthly AAM anomaly to El Niño SST anomaly (based on the Niño-3.4 index) is found to be approximately 1 angular momentum unit (=1025 kg m2 s−1) per degree Celsius for most post-1975 El Niños. This ratio is much smaller, however, during the 1965/66 and 1972/73 El Niños, raising the possibilities that either the early reanalysis data are in error due to sparse observations, or the atmospheric response to the two early El Niños was unusual. The possibility of a severe data problem in the reanalysis is ruled out by cross-validating the AAM time series with independent measurements of length of day. The latitudinal structures of the zonal wind anomalies in 1965/66 and 1972/73 are examined for both the reanalysis and a set of general circulation model (GCM) simulations. Multiple GCM runs with specified SST produce a more positive ensemble-mean AAM anomaly in 1965 than its counterpart in the reanalysis. The GCM-simulated ensemble-mean zonal wind anomaly resembles the canonical El Niño response with accelerations of subtropical zonal jets in both hemispheres, a pattern that is almost absent in the reanalysis. On the other hand, a large spread exists among the individual ensemble members in the 1965/66 GCM simulations. Although the majority of the individual ensemble members shows the canonical El Niño response, two outliers (out of 12 runs) exhibit very small zonal wind responses in the Northern Hemisphere similar to the reanalysis. Thus, the observed AAM anomaly during 1965/66 is interpreted as an outlier with atmospheric noise being strong enough to overwhelm the canonical El Niño response. The low AAM in the 1972/73 event is related in the reanalysis to a significantly negative zonal wind response on the equator. This signal is robustly reproduced, although with a slightly smaller amplitude, in the ensemble mean and all individual ensemble members in the GCM simulations. The small ensemble standard deviation and large ensemble-mean response on the equator indicate that the negative response is due to the lower-boundary forcing related to the SST anomaly. The fact that the AAM anomaly in 1972/73 is not well correlated with the Niño-3.4 index, then, indicates that SST anomalies outside the conventional El Niño region may be responsible for the low AAM. The uncharacteristically low values of global AAM in 1965/66 and 1972/73 contribute to a low mean for the decade before 1975, which, combined with high AAM in the post-1980 era, produces a significant upward trend in AAM in the second half of the twentieth century. If the weak AAM anomalies during the two pre-1975 El Niños are due to random noise or incidental non-El Niño influences, taking them at face value would result in an overestimate of about 15%–20% in the multidecadal trend of AAM due to boundary forcing alone. Notably, a multidecadal trend in AAM is also simulated in the ensemble mean of the multiple GCM runs, but its magnitude is smaller than the observed counterpart and more consistent with the multidecadal trend of the Niño-3.4 index. The implications of these findings for climate change detection are discussed. Link to Paper: https://journals.ametsoc.org/doi/pdf/10.1175/1520-0442(2003)016<2526%3AUBIAAM>2.0.CO%3B2 Credit goes to Tom @Isotherm for finding this paper - thank you.
  6. Bring Back 1962-63

    Studies of atmospheric angular momentum

    Studies of atmospheric angular momentum Authors: NOAA, Climate Diagnostics Center, Science Review Published: 25th/26th July, 2001 Chapter 4: Empirical and Process Studies Introduction to chapter 4, part 3: Atmospheric angular momentum (AAM) provides a convenient framework to study the role of mountains, surface wind stresses and various transport mechanisms in variability ranging from intraseasonal to interdecadal and beyond. Quantitative studies are feasible with current global assimilated datasets which show a good budget balance for global integrals, intraseasonal variations and during northern winter/spring. The budgets get much worse when gravity wave drag is included, if zonal integrals are considered or during summer/fall seasons. AAM is useful as an index of the large scale zonal flow since it is highly correlated with independent length-of-day measurements and with phenomena such as the QBO, ENSO, the MJO and possibly global warming. CDC scientists have examined several aspects of AAM variability, including: the link to MJO tropical convection, a linear model of global AAM and its torques, the global AAM budget imbalances due to gravity wave drag, the forcing for the semiannual seasonal component of AAM and the AAM response to global warming in an ensemble of coupled ocean-atmosphere model runs. CDC also monitors in real time the complete vertically integrated budget as part of its web-based maproom activities and distributes AAM and torque data to other researchers. Link to full paper: https://www.esrl.noaa.gov/psd/psd1/review/Chap04/sec3_body.html Link to Introduction to Chapter 4: https://www.esrl.noaa.gov/psd/psd1/review/Chap04/index.html Link to full Science Review: https://www.esrl.noaa.gov/psd/psd1/review/SciRev.pdf
  7. Bring Back 1962-63

    Where is ENSO stress balanced?

    Where is ENSO stress balanced? Authors: Matthias Münnich and David Neelin First Published: 20th November, 2003 Published online: 14th April, 2004 Abstract: The zonal surface torque budget associated with the tropical wind stress anomalies during El Niño/Southern Oscillation is analyzed. Mountain and surface stress torques over South America are found to play a prominent role. Local momentum change is negligible for 6 month averages allowing the balance among regional contributions to the torque anomalies to be compared. During El Niño, eastward torque anomalies over the central equatorial Pacific are largely compensated by westward anomalies elsewhere in the equatorial band, notably over South America. Torque anomalies over South America and the Pacific in latitude bands north and south of the equator are both westward and are not compensated within the band, implying an export of eastward momentum to higher latitudes. Copyright © 2003 Royal Meteorological Society. Published by Elsevier Ltd. All rights reserved. Link to full paper: https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1016/j.atmoscilet.2003.11.001
  8. The Effects of Mountains on the General Circulation of the Atmosphere as Identified by Numerical Experiments Authors: Syukuro Manabe and Theodore B. Terpstra Published: 26th June, 1973 Abstract: In order to identify the effects of mountains upon the general circulation of the atmosphere, a set of numerical experiments is performed by use of a general circulation model developed at the Geophysical Fluid Dynamics Laboratory of NOAA. The numerical time integrations of the model are performed with and without the effects of mountains. By comparing the structure of the model atmospheres that emerged from these two numerical experiments, it is possible to discuss the role of mountains in maintaining the stationary and transient disturbances in the atmosphere. The model adopted for this study has a global computational domain and covers both the troposphere and stratosphere. For the computation of radiative transfer, the distribution of incoming solar radiation in January is assumed. Over the ocean, the observed distribution of the sea surface temperature of February is assumed as a lower boundary condition of the model. Over the continental surface, temperature is determined such that the condition of heat balance at the ground surface is satisfied. The mountain topography is taken into consideration using the so-called σ-coordinate system in which pressure normalized by surface pressure is used as a vertical coordinate. The grid size for the computation of horizontal finite differences is chosen to be about 250 km. Nine finite-difference levels are chosen in unequal pressure intervals so that these levels can represent not only the structure of the mid-troposphere but also that of the stratosphere and the planetary boundary layer. The results of the numerical experiments indicate that it is necessary to consider the effects of mountains for the successful simulation of the stationary flow field in the atmosphere, particularly in the upper troposphere and stratosphere. As predicted by Bolin, the flow field in the upper troposphere of the mountain model has a stationary trough in the lees of major mountain ranges such as the Rocky Mountains and the Tibetan Plateau. To the east of the trough, an intense westerly flow predominates. In the stratosphere, an anticyclone develops over the Aleutian Archipelago. These features of the mountain model, which are missing in the model without mountains, are in good qualitative agreement with the features of the actual atmosphere in winter. In the model troposphere, mountains increase markedly the kinetic energy of stationary disturbances by increasing the stationary component of the eddy conversion of potential energy, whereas mountains decrease the kinetic energy of transient disturbances. The sum of the stationary and transient eddy kinetic energy is affected little by mountains. In the model stratosphere, mountains increase the amplitude of stationary disturbances partly because they enhance the energy supply from the model troposphere to the stratosphere. According to wavenumber analysis, the longitudinal scale of eddy conversion in the model atmosphere increases significantly due to the effects of mountains. This increase results mainly from the large increase of stationary eddy conversion which takes place at very low wavenumbers. The results of the analysis reveal other important effects of mountains. For example, the probability of cyclogenesis in the model atmosphere increases significantly on the lee side of major mountain ranges where the core of the westerly jet is located. Also, mountains affect the hydrologic processes in the model atmosphere by modifying the field of three-dimensional advection of moisture, and alter the global distribution of precipitation very significantly. In general, the distribution of the model with mountains is less zonal and more realistic than that of the model without mountains. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/1520-0469(1974)031<0003%3ATEOMOT>2.0.CO%3B2
  9. Bring Back 1962-63

    Topographic Instability: Tests

    Topographic Instability: Tests Authors: Joseph Egger and Klaus-Peter Hoinka Published: 16th May, 2007 Abstract: Theories of topographic instability predict growth of perturbations of mean flow and wave modes due to their interaction with mountains under favorable conditions. Mountain torques form an important part of this interaction. It has been suggested that topographic instabilities contribute significantly to the subseasonal variability of the atmosphere but observational tests of topographic instability mechanisms have not yet been performed. Greenland is selected as a test bed because of its isolation, simple shape, and appropriate size. The observed flow development during mountain torque events is investigated in terms of a regression analysis. Changes of axial angular momentum and zonal mean wind with respect to the torques are monitored for domains covering Greenland since the acceleration (deceleration) of the regional zonal flow in response to a positive (negative) torque is a key feature of topographic instability. In particular, southern and northern analysis domains are considered separately in order to test “dipole” instability theories in addition to “monopole” situations where the meridional extent of the pressure perturbations is similar to that of Greenland. Moreover, zonal bands are used as analysis domains. It is found that the response of the zonal wind to the torques is quite small and not systematic. There is no evidence of monopole or dipole topographic instability. A less detailed analysis for the Tibetan Plateau leads to the same result. Reasons for these negative outcomes are discussed as are shortcomings of the tests. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/2007JAS2311.1
  10. The remote effect of the Tibetan Plateau on downstream flow in early summer Authors: Yafei Wang, Xiangde Xu, Anthony R. Lupo, Pingyun Li and Zhicong Yin Published: 11th October, 2011 Abstract: By using numerical experiments and observational data, this study examined the uplifting and thermal effects of the Tibetan Plateau (TP) on downstream airflow in early summer. Our principal finding is that the uplifting effect of the TP in an Atmospheric General Climate Model (AGCM), including air made warmer than its surroundings climatologically by the huge topography, results mainly in a local response in the atmosphere, i.e., a large ridge north of the TP in the troposphere in June. There was no Rossby wave response to the uplifting effect. However, simulations and statistical analyses strongly suggested that the anomalous TP atmospheric heating associated with global climate warming tends to excite a Rossby wave originating from the TP via Lake Baikal and continuing to move through the Okhotsk Sea to downstream areas. The appearance of the Rossby wave coincides with the positive phase of the eastern part of a normal stationary wave originating in the Caspian Sea traveling via the Okhotsk Sea to the sea area east of Japan that often occurs in June. Thus the TP atmospheric heating acts as an additional wave source in relaying and enhancing the eastern part of the normal wave propagation. Its path usually lies beyond 40°N latitude, which is where the westerly jet stream takes over the role of waveguide. Link to full paper: https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2011JD015979
  11. The intraseasonal atmospheric angular momentum associated with MJO convective initiations Authors: Naoko Sakaeda and Paul E. Roundy Published: 14th January, 2016 Abstract: The first part of this study examines the driving mechanisms of the equatorial intraseasonal relative atmospheric angular momentum (AAM) and its dynamical relationship to the upper‐tropospheric zonal wind over the Western Hemisphere (WH) during the convective initiation of the Madden–Julian Oscillation (MJO) over the Indian Ocean. The budget analysis shows that the main driver of the equatorial intraseasonal AAM anomaly is the meridional transport of momentum induced by the modulation of the background subtropical eddies by the intraseasonal eddies. While the subtropical eddies over the central Pacific basin partly drive the equatorial AAM by meridionally transporting the momentum, the equatorial zonal wind associated with the same subtropical eddies is zonally advected and locally amplified over the east Pacific and Atlantic basins. The common source phenomena that transport momentum result in simultaneous evolution of the WH upper‐tropospheric zonal wind and the AAM on intraseasonal time‐scales, but their main driving mechanisms are different. The second part of the study investigates the influence of the equatorial intraseasonal AAM state on the subsequent development of initiating MJO convection over the Indian Ocean. In the presence of the WH upper‐tropospheric easterly wind, MJO convection tends to develop a stronger enhanced convective envelope when the initiation occurs during the negative intraseasonal AAM state, which strengthens and extends the upper‐tropospheric easterly wind in the WH. When the AAM anomaly is positive, it tends to induce stronger mid‐tropospheric convergence above the region of convective initiation, thereby suppressing the lower‐tropospheric updraught and suppressing the further growth of convection. The results show that the combined effects of the WH circumnavigating circulation and the AAM can influence the subsequent development of MJO convection over the Indian Ocean. Link to full paper: This paper is behind a paywall. The article was from the RMS Quarterly Journal. Here's a link to their website: https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/qj.2740
  12. Atmospheric forcing mechanisms of polar motion Authors: J Stuck, Florian Seitz and Mick Thomas Published: January, 2005 Abstract: The polar motion consists of free and forced oscillations which are influenced by mass variations in the Earth system. The contribution of the atmosphere to the excitation of the polar motion is investigated by forcing the dynamic Earth system model DyMEG with atmospheric angular momentum (AAM) and by multivariate statistical analyses of the regional representation of the AAM. The analyses are performed with the ECHAM3-T21 and the ECHAM4-T42 global circlation models, which are only forced by observed sea surface temperatures. For validation, the NCEP-reanalysis is used. The model results of DyMEG show, that the annual oscillation of polar motion is predominantly due to atmospheric pressure forcing, while the motion component is less important. A regional statistical analysis of the AAM due to mass variations presents an anomaly pattern which consists of strong annual pressure variations located over Asia, in particular at the Himalaya. This annual atmospheric pushing and pulling on the Earth above the Asian continent turns out to be the primary component responsible for accelerating the forced polar motion. These pressure variations are also active on higher frequencies connected with rapid polar motions. The results reveals, that atmospheric forcing is sufficient to excite the Chandler wobble (CW). Neither a significant nor at least an increased signal in the frequency domain of 14 to 16 months exists and regional statistical analysis of AAM give no hint for an oscillation with a typical time scale of 14 to 16 months. Hence, the CW seems to be excited by stochastic processes in the atmosphere. Link to full paper: https://mediatum.ub.tum.de/doc/1300596/file.pdf
  13. Atmospheric torques and Earth’s rotation: what drove the millisecond-level length-of-day response to the 2015–2016 El Niño? Authors: Sébastien B. Lambert, Steven L. Marcus and Olivier de Viron Published: 14th November, 2017 Abstract El Ninõ-Southern Oscillation (ENSO) events are classically associated with a significant increase in the length of day (LOD), with positive mountain torques arising from an east-west pressure dipole in the Pacific driving a rise of atmospheric angular momentum (AAM) and consequent slowing of the Earth's rotation. The large 1982-1983 event produced a lengthening of the day of about 0.9 ms, while a major ENSO event during the 2015-2016 winter season produced an LOD excursion reaching 0.81 ms in January 2016. By evaluating the anomaly in mountain and friction torques, we found that (i) as a mixed eastern-central Pacific event, the 2015-2016 mountain torque was smaller than for the 1982-1983 and 1997-1998 events, which were pure eastern Pacific events, and (ii) the smaller mountain torque was compensated for by positive friction torques arising from an enhanced Hadley-type circulation in the eastern Pacific, leading to similar AAM-LOD signatures for all three extreme ENSO events. The 2015-2016 event thus contradicts the existing paradigm that mountain torques cause the Earth rotation response for extreme El Ninõ events. Link to full paper: https://www.earth-syst-dynam.net/8/1009/2017/esd-8-1009-2017.pdf
  14. Planetary‐scale wave activity as a source of varying tropospheric response to stratospheric sudden warming events: A case study Authors: Patrick Martineau and Seok‐Woo Son Published: 3rd October, 2013 Abstract: Stratospheric Sudden Warming (SSW) events are typically, but not always, accompanied by negative Northern Annular Mode anomalies in the troposphere. However, large uncertainties remain as to which dynamical processes are responsible for those anomalies. In order to highlight sources of variability in stratosphere‐troposphere coupling among SSW events, we present a case study of three selected events and show detailed Transformed Eulerian Mean diagnostics for momentum changes in the stratosphere and troposphere in the course of those events. Our results suggest that planetary‐scale waves, especially the zonal wave number 2 component, may play an important role not only for the onset of tropospheric anomalies in response to SSW events but also for introducing variability in the vertical coupling, i.e., whether the tropospheric circulation anomalies lag, lead, or occur simultaneous to the weakening of the vortex. Particularly, the meridional propagation of those waves in the upper troposphere could be an important factor that determines whether SSW events lag or lead tropospheric anomalies. Link to full paper: https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/jgrd.50871
  15. The Angular Momentum Budget of the Transformed Eulerian Mean Equations Authors: Joseph Egger and Klaus-Peter Hoinka Published: 24th April, 2008 Abstract: The axial angular momentum (AAM) budget of zonal atmospheric annuli extending from the surface to a given height and over meridional belts is discussed within the framework of conventional and transformed Eulerian mean (TEM) theory. Conventionally, it is only fluxes of AAM through the boundaries and/or torques at the surface that are able to change the AAM of an annulus. TEM theory introduces new torques in the budget related to the vertically integrated Eliassen–Palm flux divergence and also new AAM fluxes of the residual difference circulation. Some of these torques are displayed for various annuli. In particular, the application of TEM theory generates a large positive torque at tropospheric upper boundaries in the global case. This torque is much larger than the global mountain and friction torques but is cancelled exactly by the new vertical AAM fluxes through the upper boundary. It is concluded that the TEM approach complicates the analysis of AAM budgets but does not provide additional insight. Isentropic pressure torques are believed to be similar to the TEM torques at the upper boundary of an annulus. The isentropic pressure torques are evaluated from data and found to differ in several respects from the TEM torques. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/2008JAS2725.1
  16. Torques and the Related Meridional and Vertical Fluxes of Axial Angular Momentum Authors: Joseph Egger and Klaus-Peter Hoinka Published: 21st July, 2004 Abstract: The budget equation of the zonally averaged angular momentum is analyzed by introducing belts of 1000-km width to cover the meridional plane from pole to pole up to an altitude of 28 km. Using ECMWF Re-Analysis (ERA) data the fluxes of angular momentum are evaluated as well as the mountain and friction torques per belt. Generalized streamfunctions and velocity potentials are introduced to better depict the fluxes related to the angular momentum transferred at the ground during an event of mountain or friction torque. The variance of the total flux divergence per belt is one order of magnitude larger than those of the torques. All variances peak at midlatitudes. As a rule, the structure of the generalized streamfunctions changes little during an event; that is, the structure of the nondivergent part of the fluxes is stable. That of the divergent part, as represented by the velocity potential, undergoes a rapid change near the peak of a torque event. Positive friction torque events in midlatitude belts are preceded by a divergence of angular momentum fluxes in that belt, which is linked to the anticyclonic mass circulation needed to induce the positive torque. The divergence in the belt breaks down shortly before the torque is strongest. Angular momentum is transported upward from the ground after that. Much of the angular momentum generated in a midlatitude belt by positive mountain torques is transported out of the domain, but there is also a short burst of upward transports. Angular momentum anomalies linked to torque events near the equator tend to be symmetric with respect to the equator. Related fluxes affect the midlatitudes of both hemispheres. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/MWR-2870.1
  17. Bring Back 1962-63

    Isentropic Pressure and Mountain Torques

    Isentropic Pressure and Mountain Torques Authors: Joseph Egger and Klaus-Peter Hoinka Published: 12th March, 2009 Abstract: The relation of pressure torques and mountain torques is investigated on the basis of observations for the polar caps, two midlatitude and two subtropical belts, and a tropical belt by evaluating the lagged covariances of these torques for various isentropic surfaces. It is only in the polar domains and the northern midlatitude belts that the transfer of angular momentum to and from the earth at the mountains is associated with pressure torques acting in the same sense. The situation is more complicated in all other belts. The covariances decline with increasing potential temperature (height). The role of both torques in the angular momentum budget of a belt is discussed. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/2009MWR2848.1
  18. Axial Angular Momentum: Vertical Fluxes and Response to Torques Authors: Joseph Egger and Klaus-Peter Hoinka Published: 4th November, 2003 Abstract: The horizontally averaged global angular momentum μ at a certain height reacts only to the vertical divergence of the angular momentum flux at least above the crest height of the earth's orography. The flux is tied to the torques at the surface. Data are used to evaluate the flux and the response of μ to the torques. It is shown that the accuracy of the data is sufficient for an investigation of this interaction. It is found that the horizontally averaged angular momentum in the upper troposphere and lower stratosphere tends to be negative before an event of positive friction torque. Downward transports of negative angular momentum from these layers allow the angular momentum to further decrease near the ground, even shortly before the event although the friction torque is positive at that time. The impact of the mountains during this process is demonstrated. The ensuing positive response to the friction torque is felt throughout the troposphere. The final decay of this reaction involves downward transports of μ with typical velocities of ∼1–2 km day−1. The angular momentum in the lower troposphere tends to be negative before an event of positive mountain torque. There is a short burst of rapid upward transport of positive angular momentum during the event itself, which reaches the stratosphere within 1–2 days. A phase of decay follows with slow downward transport of positive angular momentum. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/1520-0493(2004)132<1294%3AAAMVFA>2.0.CO%3B2
  19. Latitude–Height Structure of the Atmospheric Angular Momentum Cycle Associated with the Madden–Julian Oscillation Authors: Joseph Egger and Dr Klaus Weickmann Published: 9th June, 2006 Abstract: The angular momentum cycle of the Madden–Julian oscillation is analyzed by regressing the zonally averaged axial angular momentum (AAM) budget including fluxes and torques against the first two principal components P1 and P2 of the empirical orthogonal functions (EOFs) of outgoing longwave radiation (OLR). The maximum of P1 coincides with an OLR minimum near 150°E and a shift from anomalously negative AAM to positive AAM in the equatorial troposphere. AAM anomalies of one sign develop first in the upper-equatorial troposphere and then move downward and poleward to the surface of the subtropics within two weeks. During the same time the opposite sign AAM anomaly develops in the upper-equatorial troposphere. The tropical troposphere is warming when P1 approaches its maximum while the stratosphere is cooling. The torques are largest in the subtropics and are linked with the downward and poleward movement of AAM anomalies. The evolution is conveniently summarized using a time–height depiction of the global mean AAM and vertical flux anomaly. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/MWR3363.1
  20. The Dynamics of Intraseasonal Atmospheric Angular Momentum Oscillations Authors: Dr Klaus M. Weickmann, George N. Kiladis and Prashant D. Sardeshmuykh Published: 17th October, 1996 Abstract: The global and zonal atmospheric angular momentum (AAM) budget is computed from seven years of National Centers for Environmental Prediction data and a composite budget of intraseasonal (30–70 day) variations during northern winter is constructed. Regressions on the global AAM tendency are used to produce maps of outgoing longwave radiation, 200-hPa wind, surface stress, and sea level pressure during the composite AAM cycle. The primary synoptic features and surface torques that contribute to the AAM changes are described. In the global budget, the friction and mountain torques contribute about equally to the AAM tendency. The friction torque peaks in phase with subtropical surface easterly wind anomalies in both hemispheres. The mountain torque peaks when anomalies in the midlatitude Northern Hemisphere and subtropical Southern Hemisphere are weak but of the same sign. The picture is different for the zonal mean budget, in which the meridional convergence of the northward relative angular momentum transport and the friction torque are the dominant terms. During the global AAM cycle, zonal AAM anomalies move poleward from the equator to the subtropics primarily in response to momentum transports. These transports are associated with the spatial covariance of the filtered (30–70 day) perturbations with the climatological upper-tropospheric flow. The zonally asymmetric portion of these perturbations develop when convection begins over the Indian Ocean and maximize when convection weakens over the western Pacific Ocean. The 30–70-day zonal mean friction torque results from 1) the surface winds induced by the upper-tropospheric momentum sources and sinks and 2) the direct surface wind response to warm pool convection anomalies. The signal in relative AAM is complemented by one in “Earth” AAM associated with meridional redistributions of atmospheric mass. This meridional redistribution occurs preferentially over the Asian land mass and is linked with the 30–70-day eastward moving convective signal. It is preceded by a surface Kelvin-like wave in the equatorial Pacific atmosphere that propagates eastward from the western Pacific region to the South American topography and then moves poleward as an edge wave along the Andes. This produces a mountain torque on the Andes, which also causes the regional and global AAM to change. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/1520-0469(1997)054<1445%3ATDOIAA>2.0.CO%3B2
  21. What is the GSDM and how does it help with subseasonal weather forecasts? A YouTube Presentation Presentation By: Edward K Berry (Senior Weather-Climate Scientist) Presentation Event: American Meteorology Society - Student Chapter, College of DuPage, Chicago Presentation Date: 28th March, 2018 Summary: Leading meteorological scientists Ed Berry and Dr Klaus Weickmann jointly developed their GSDM (Global Synoptic Dynamic Model) while they were working at NOAA in the late 1990s and earlier years of this century. They also devised the GWO (Global Wind Oscillation) as a way of plotting and measuring the amounts of relative global AAM (Atmospheric Angular Momentum), frictional torque and mountain torque at different phases of the cycle. They became leaders in this specialist research which has been used to assist in understanding impacts on global weather patterns and upcoming changes up to a few weeks ahead. They left NOAA several years ago and Klaus Weickmann has retired. Ed Berry continues his excellent work on the GSDM and retains his lifelong passion to develop the model and its meteorological applications further. He recently gave a brilliant presentation about the model at an AMS meeting in Chicago. This is a one hour seminar with clear charts and explanations, ending with a question and answer session. I have watched it three times already and understand a little more about the GSDM from each viewing. For anyone wishing to learn more about AAM, the torques, the GWO and how they interact with other major teleconnections like phases of the ENSO (El Nino Southern Oscillation) and the MJO (Madden Julian Oscillation) then this is absolutely essential viewing. I also strongly recommend this for more advanced viewers as well. The presentation is right up-to-date and includes the 2018 SSW (Sudden Stratospheric Warming) event and links to key issues like climate change. Much of the presentation is slanted towards the North American climate and US weather patterns but it has a global significance and includes impacts on both hemispheres. Link to full presentation (1 hour and 4 minutes): https://youtu.be/Cv5CblXbYuQ I also reviewed this presentation on the main "Telconnections: A More technical Discussion" thread. This includes some examples of the charts used in the presentation. Click on this direct link to page 3 of the thread which contains the review (it is just over halfway down that page): https://www.33andrain.com/topic/868-teleconnections-a-more-technical-discussion/?page=3
  22. Mountains, the Global Frictional Torque, and the Circulation over the Pacific–North American Region Authors: Klaus Weickmann Published: 2nd April, 2003 Abstract: The global mountain (τM ) and frictional (τF ) torques are lag correlated within the intraseasonal band, with τF leading τM. The correlation accounts for 20%–45% of their variance. Two basic feedbacks contribute to the relationship. First, the mountain torque forces global atmospheric angular momentum (AAM) anomalies and the frictional torque damps them; thus, dτF/dt ∝ −τM. Second, frictional torque anomalies are associated with high-latitude sea level pressure (SLP) anomalies, which contribute to subsequent mountain torque anomalies; thus, dτM/dt ∝ τF. These feedbacks help determine the growth and decay of global AAM anomalies on intraseasonal timescales. The low-frequency intraseasonal aspect of the relationship is studied for northern winter through lag regressions on τF. The linear Madden–Julian oscillation signal is first removed from τF to focus the analysis on midlatitude dynamical processes. The decorrelation timescale of τF is similar to that of teleconnection patterns and zonal index cycles, and these familiar circulation features play a prominent role in the regressed circulation anomalies. The results show that an episode of interaction between the torques is initiated by an amplified transport of zonal mean–zonal momentum across 35°N. This drives a dipole pattern of zonal mean–zonal wind anomalies near 25° and 50°N, and associated SLP anomalies. The SLP anomalies at higher latitudes play an important role in the subsequent evolution. Regionally, the momentum transport is linked with large-scale eddies over the east Pacific and Atlantic Oceans that have an equivalent barotropic vertical structure. As these eddies persist/amplify, baroclinic wave trains disperse downstream over North American and east Asian topography. The wave trains interact with the preexisting, high-latitude SLP anomalies and drive them southward, east of the mountains. This initiates a large monopole mountain torque anomaly in the 20°–50°N latitude band. The wave trains associated with the mountain torque produce additional momentum flux convergence anomalies that 1) maintain the zonal wind anomalies forced by the original momentum transport anomalies and 2) help drive a global frictional torque anomaly that counteracts the mountain torque. Global AAM anomalies grow and decay over a 2-week period, on average. Over the Pacific–North American region, the wave trains evolve into the Pacific–North American (PNA) pattern whose surface wind anomalies produce a large portion of the compensating frictional torque anomaly. Case studies from two recent northern winters illustrate the interaction. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/1520-0493(2003)131<2608%3AMTGFTA>2.0.CO%3B2
  23. Tornado Frequency in the United States Related to Global Relative Angular Momentum Authors: Vittorio A. Gensini, Alan Marinaro Published: Feb 2016 Abstract: Global relative angular momentum and the first time derivative are used to explain nearly an order of magnitude of the variability in 1994–2013 U.S. boreal spring tornado occurrence. When plotted in a phase space, the global wind oscillation (GWO) is obtained. This global index accounts for changes in the global budget of angular momentum through interactions of tropical convection anomalies and extratropical dynamics including the engagement of surface torques. It is shown herein that tornadoes are more likely to occur in low angular momentum base states and less likely to occur in high angular momentum base states. When excluding weak GWO days, a maximum average of 3.9 (E)F1+ tornadoes per day were found during phase 1. This decreases to a minimum of 0.9 (E)F1+ tornadoes per day during phase 5. Composite environmental analysis suggests that increases/decreases in tornado occurrence are closely associated with anomalies in tropospheric ingredients necessary for tornadic storms. In addition, tornado frequency days exceeding the 90th percentile are shown to be favored when the global relative angular momentum budget and first time derivative are negative (GWO phases 1 and 2), as are significant tornado events [(E)F2+]. Implications for using GWO as a predictor for tornado forecasting are also discussed. Link to full paper: https://journals.ametsoc.org/doi/full/10.1175/MWR-D-15-0289.1
  24. Uncertainty analysis of atmospheric friction torque on the solid Earth Authors: Haoming Yan and Yong Huang First Published: 11th December, 2015 Abstract: The wind stress acquired from European Centre for Medium-Range Weather Forecasts (ECMWF), National Centers for Environmental Prediction (NCEP) climate models and QSCAT satellite observations are analyzed by using frequency-wavenumber spectrum method. The spectrum of two climate models, i.e., ECMWF and NCEP, is similar for both 10 m wind data and model output wind stress data, which indicates that both the climate models capture the key feature of wind stress. While the QSCAT wind stress data shows the similar characteristics with the two climate models in both spectrum domain and the spatial distribution, but with a factor of approximately 1.25 times larger than that of climate models in energy. These differences show the uncertainty in the different wind stress products, which inevitably cause the atmospheric friction torque uncertainties on solid Earth with a 60% departure in annual amplitude, and furtherly affect the precise estimation of the Earth's rotation. Link to Paper: https://ac.els-cdn.com/S1674984716300301/1-s2.0-S1674984716300301-main.pdf?_tid=c9f4e787-e0d8-4df2-9487-e526cbdd54a5&acdnat=1523641140_b6c42688efd8a36f8864cb62251c7c61
  25. Dynamic coupling of the stratosphere with the troposphere and sudden stratospheric warmings Author: Kevin E. Trenberth First Published: 1966 (revised 5th July, 1972 and published 1st April ,1973) Abstract: Numerical time integrations of a 9-layer quasigeostrophic highly truncated spectral model of the atmosphere are used to study tropospheric-stratospheric interaction with particular regard to sudden stratospheric warmings. The model is global and extends to 0.05 mb (71 km) with roughly 10 km resolution in the stratosphere, and includes an annual heating cycle. A linear baroclinic analysis of a similar model shows that the inclusion of spherical geometry allows significant growth rates in the long wave region of instability. Preliminary integrations without eddies reveal the seasonal variation of a thermally driven circulation. Model integrations simulating the months of December and January were made (i) without nonzonal forcing, and (ii) with nonzonal heating and orography included, to represent southern and northern hemisphere winters. The overall features of the atmosphere were very well simulated. With the inclusion of the annual heating cycle, the model successfully reproduced a more intense circulation in January than existed in December. This caused a maximum tropospheric meridional temperature gradient in the winter hemisphere to occur some weeks prior to the maximum in the external heating field. The presence of nonzonal heating in the winter hemisphere brought about an increase in circulation intensity and produced a stationary perturbation with a strong westward slope with height extending high into the stratosphere. These are features somewhat similar to those of the Aleutian system. Associated with this were considerably warmer temperatures in the polar night stratosphere and a weaker stratospheric westerly jet. The winter mesosphere of the model was driven in the manner of the lower stratosphere and a temperature maximum was produced in mid latitudes. Link to Paper: ftp://ftp.library.noaa.gov/docs.lib/htdocs/rescue/mwr/101/mwr-101-04-0306.pdf
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