Showing results for tags 'aam'. - 33andrain Weather Discussion Community Jump to content

Search the Community

Showing results for tags 'aam'.

More search options

  • Search By Tags

    Type tags separated by commas.
  • Search By Author

Content Type


  • General Weather Discussion
    • Forecasting and Discussion
    • 33andrain's Wx Research Portal
    • Ask the Experts!
    • Archived Storm Threads
  • Off Topic
  • Wx Retrospectives & Memories's Topic Directory
  • 45andbeyond's Political Discussion Topics
  • NY Yankees's Topic Directory
  • NY Mets's Mets Discussion Topics
  • NY Giants's Giants Discussion Topics
  • Post Memes / Animated GIFs's Memes / GIFs
  • NY Jets's Jets Discussion Topics
  • Movie & TV Lounge's TV/Movies Posts
  • Snap and Share - Weather and Outdoor Photography's Photos
  • Off Topic's General Discussion
  • The Foodie Network's Food Discussion Topics
  • General NFL Discussion's NFL Posts
  • Lock...It...In...'s Topics

Product Groups

  • Premium Services
  • Winter Essentials

Find results in...

Find results that contain...

Date Created

  • Start


Last Updated

  • Start


Filter by number of...


  • Start



About Me


How did you find out about us?

Found 37 results

  1. Links Section In This Post, below the intro. I have been recently asked to start a thread, to talk about weather teleconnections and similar topics. This is often a topic not very well discussed on other weather places, and places like Twitter. We have a number of experts, enthusiasts, and meteorologists, who are knowledgeable in this area. So this is a thread for technical discussion about the teleconnections, etc, as well as a place for questions about these topics. We need to start talking about these climate drivers more, as they are the key to unlocking medium-long term forecasts. We are making a place for technical discussion about these factors away from the main thread/s. So this thread is born. Teleconnections that could be up for discussion are: MJO, AAM/GWO, NAO, RRWT, NP jet, Mountain & Frictional Torques, AO/AAO, ENSO, IOD, AMO, SSTs in general, SOI, QBO, the Stratosphere, etc. Feel free to talk about related topics, but stick to this general topic. I encourage all posters to discuss and pose questions relating to the topic, and keep it a relaxed atmosphere. Any questions, just PM me or comment here. Hope we can make this work Links Section ERSL Link, Up to 24 hours behind. GWO 90 day Victor Gensini Site. 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. MJO Composites:
  2. Spatial and temporal variations of global frictional torque during the period 1948–2011 Authors: He Gong, Mei Huang, Lin Zhu, Shengli Guo and Yaping Shao 4th March, 2016 First Published: 4th March, 2016 Abstract: Frictional torque is an important mean for momentum exchange between the atmosphere and earth, and significantly influences the variation in atmospheric angular momentum. Using NCEP-NCAR reanalysis data for the period 1948–2011, we examined the spatial and temporal patterns of frictional torque. It was found that the globally integrated frictional torque turned from positive to negative in 1972, suggesting that angular momentum was transferred from the earth to the atmosphere before 1972, but from the atmosphere to the earth thereafter. The global frictional torque steadily declined from 1948 to 1994, but has been increasing since 1995. It was also found that the global frictional torque is mainly determined by the wind systems in the mid and low latitudes of the Southern Hemisphere (SH), where large changes in frictional torque occurred during the study period. Westerly wind increased continuously in the midlatitudes after 1948, while easterly wind decreased in the tropics of the SH after the 1980s. Link to full paper: The "Springer Link" access is behind a paywall but I found this link via the Chinese Meteorological Society:
  3. Estimates of Atmospheric Angular Momentum, Friction, and Mountain Torques during 1987–1988 Authors: R. A. Madden and P. Speth First Published: 1st November, 1995 Abstract: Atmospheric angular momentum (M), friction (TF), and mountain torques (TM) are estimated from a 13-month period of European Centre for Medium-Range Weather Forecasts (ECMWF) data. Cross-spectrum analysis between M and total torques results in high coherence and one-quarter cycle phase angles (TF + TM leading M) for timescales between 5 and 66 days, suggesting that variations of the total torque are reasonably well estimated for these slower variations. However, cross spectra between M and TF, and TM separately reveal that the relatively high coherence is present between M and TF only at periods longer than 20 days. Also comparison with other published values and the considerable lack of balance between TF + TM and M over a full year implies that our estimates of TF, based on the parameterization of surface wind stress in short-term forecasts of the ECMWF, are negatively biased. For the 13-month period, the average bias is about −15.2 Hadleys (1018 kg m2 s−2). During the period there are a few near 50-day oscillations in the M. Similar variations have been reported before and related to tropical intraseasonal oscillations of the same timescale. Two oscillations in M that are coincident with eastward-propagating cloud complexes of tropical intraseasonal oscillations are examined more closely. It is found that TF and TM work together to alter the M on the 50-day timescale, but that TM's contribution is three times larger than that of TF. During the two oscillations TF, reaches maxima when cloud complexes of tropical intraseasonal oscillations are in the vicinity of 90°E. It then declines but maintains positive anomalies at least until the cloud complexes reach the Central Pacific. The M reaches its maxima shortly thereafter. TM has sharp minima shortly before the cloud complexes are strongly developed in the Indian Ocean. Contributors to these minima are strong cast to west pressure gradients primarily across the Rocky Mountains. Link to full paper:<3681%3AEOAAMF>2.0.CO%3B2
  4. Name The Earth’s Atmospheric Angular Momentum Budget and its Representation in Reanalysis Observation Datasets and Climate Models Author Simon Driscoll Publication Date August 2010 Abstract Angular Momentum is a fundamental quantity in any rotating system. In this disser- ation we are predominantly concerned with the theory of conservation of angular momen- tum in the Earth’s Atmosphere, and whether this theory is represented in the National Oceanic and Atmospheric Administration’s (NOAA’s) Twentieth Century Reanalysis Ver- sion 2 Observation Dataset, the Hadley Centre’s HadCM3 and HadGEM1 climate models, and the NOAA’s GFDL CM2.0 climate model. By doing this we gain useful information as to whether the reanalysis observation dataset has internally consistent physics after the data assimilation process and the parameterization of variables, and we can also gain use- ful information as to whether a climate model (that does not require the data assimilation phase) has correct parametrizations of variables and internally consistent physics. We find that the NOAA Reanalysis Observation Dataset does not conserve angular momentum, and that the torques are the major source of error. There is error in all torques, especially during the northern hemisphere winter. The little change in the latitudinal torque profiles for the reanalysis observation dataset, calculated for 1890-1899 and 1990- 1999, suggests that with the aid of the reanalysis process a very poor observation network can give the same latitudinal torque profiles as the observation network of today. It is also found that the HadCM3 model has a serious error in its representation of the mountain torque, and we note with great interest that the climate model HadGEM1 (who’s physical processes were developed from HadCM3) has significantly smaller values in its regional friction torque than that of HadCM3. Indeed all the other latitudinal profiles calculated in this dissertation, implying the surface winds are too weak, and even suggest- ing there may be differences in the whole circulation between HadGEM1 and HadCM3. We also find error in the spatial patterns of the torques of the NOAA GFDL CM2.0 model whose near symmetric torques imply that the circulation throughout the atmosphere is likely to be symmetric about the equator, thus the northern hemisphere circulation is the same as that of the southern hemisphere in the model. Link to original paper;rep=rep1&amp;type=pdf
  5. 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: Credit goes to Eric @Webberweather for finding this presentation - thank you.
  6. 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: Credit goes to Tom @Isotherm for finding this paper - thank you.
  7. 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:
  8. 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:<2526%3AUBIAAM>2.0.CO%3B2 Credit goes to Tom @Isotherm for finding this paper - thank you.
  9. 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:
  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:
  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:
  12. 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:
  13. 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:
  14. 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:
  15. 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:
  16. 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:
  17. 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:<1294%3AAAMVFA>2.0.CO%3B2
  18. 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:
  19. 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:<1445%3ATDOIAA>2.0.CO%3B2
  20. 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): 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. Just click on this direct link: What is the GSDM and how does it help with subseasonal weather forecasts? - A Review of This Presentation
  21. 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:<2608%3AMTGFTA>2.0.CO%3B2
  22. 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:
  23. 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:
  24. 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:
  25. Stochastic and oscillatory forcing of global atmospheric angular momentum Authors: Weickmann, K.M., W.A. Robinson, and C. Penland First Published: 27th June, 2000 Abstract: The temporal variability and forcing of global atmospheric angular momentum (AAM) is studied using a three‐component Markov model derived from observed statistics of global AAM and the global torques. The model consists of stochastic forcing by the mountain (τM) and friction (τ *F) torque plus a pervasive negative feedback on AAM by the friction torque. AAM anomalies are damped at a 30‐day timescale and forced by torques having 1.5‐day ( τM) and 6‐day (τ *F) decorrelation timescales. A large portion of the intraseasonal variance and covariance of AAM, τM, and τF is accounted for by the Markov model. Differences between the modeled and the observed covariances are maximized in the 10‐ to 90‐day band and account for 10–30% of the variance when using data not stratified by season. An especially prominent deviation from the Markov model is the oscillatory forcing of AAM by the frictional torque at 30‐ to 60‐day periods. Additionally, there is greater coherent variance between τF and τM across the entire 10‐ to 90‐day band, with the frictional torque leading the mountain torque. This “feedback” between the global torques results from physical processes not represented in the Markov model. The synoptic characteristics of the stochastic mountain and frictional torques and of the oscillatory Madden‐Julian Oscillation are described. Link to Paper:
  • Create New...