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  • American Meteorological Society  (8)
  • 1
    Online Resource
    Online Resource
    THORPEX Research and the Science of Prediction
    American Meteorological Society ; 2017
    In:  Bulletin of the American Meteorological Society Vol. 98, No. 4 ( 2017-04-01), p. 807-830
    Details
    In: Bulletin of the American Meteorological Society, American Meteorological Society, Vol. 98, No. 4 ( 2017-04-01), p. 807-830
    Abstract: The Observing System Research and Predictability Experiment (THORPEX) was a 10-yr, international research program organized by the World Meteorological Organization’s World Weather Research Program. THORPEX was motivated by the need to accelerate the rate of improvement in the accuracy of 1-day to 2-week forecasts of high-impact weather for the benefit of society, the economy, and the environment. THORPEX, which took place from 2005 to 2014, was the first major international program focusing on the advancement of global numerical weather prediction systems since the Global Atmospheric Research Program, which took place almost 40 years earlier, from 1967 through 1982. The scientific achievements of THORPEX were accomplished through bringing together scientists from operational centers, research laboratories, and the academic community to collaborate on research that would ultimately advance operational predictive skill. THORPEX included an unprecedented effort to make operational products readily accessible to the broader academic research community, with community efforts focused on problems where challenging science intersected with the potential to accelerate improvements in predictive skill. THORPEX also collaborated with other major programs to identify research areas of mutual interest, such as topics at the intersection of weather and climate. THORPEX research has 1) increased our knowledge of the global-to-regional influences on the initiation, evolution, and predictability of high-impact weather; 2) provided insight into how predictive skill depends on observing strategies and observing systems; 3) improved data assimilation and ensemble forecast systems; 4) advanced knowledge of high-impact weather associated with tropical and polar circulations and their interactions with midlatitude flows; and 5) expanded society’s use of weather information through applied and social science research.
    Type of Medium: Online Resource
    ISSN: 0003-0007 , 1520-0477
    URL: Article
    URL: Article
    DOI: 10.1175/BAMS-D-14-00025.1
    DOI: 10.1175/BAMS-D-14-00025.2
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2017
    detail.hit.zdb_id: 2029396-3
    detail.hit.zdb_id: 419957-1
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  • 2
    Online Resource
    Online Resource
    Atmospheric Rivers Emerge as a Global Science and Applications Focus
    American Meteorological Society ; 2017
    In:  Bulletin of the American Meteorological Society Vol. 98, No. 9 ( 2017-09-01), p. 1969-1973
    Details
    In: Bulletin of the American Meteorological Society, American Meteorological Society, Vol. 98, No. 9 ( 2017-09-01), p. 1969-1973
    Type of Medium: Online Resource
    ISSN: 0003-0007 , 1520-0477
    URL: Article
    DOI: 10.1175/BAMS-D-16-0262.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2017
    detail.hit.zdb_id: 2029396-3
    detail.hit.zdb_id: 419957-1
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  • 3
    Online Resource
    Online Resource
    HyMeX: A 10-Year Multidisciplinary Program on the Mediterranean Water Cycle
    American Meteorological Society ; 2014
    In:  Bulletin of the American Meteorological Society Vol. 95, No. 7 ( 2014-07), p. 1063-1082
    Details
    In: Bulletin of the American Meteorological Society, American Meteorological Society, Vol. 95, No. 7 ( 2014-07), p. 1063-1082
    Type of Medium: Online Resource
    ISSN: 0003-0007 , 1520-0477
    URL: Article
    DOI: 10.1175/BAMS-D-12-00242.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2014
    detail.hit.zdb_id: 2029396-3
    detail.hit.zdb_id: 419957-1
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  • 4
    Online Resource
    Online Resource
    Flow-Dependent Reliability: A Path to More Skillful Ensemble Forecasts
    American Meteorological Society ; 2018
    In:  Bulletin of the American Meteorological Society Vol. 99, No. 5 ( 2018-05), p. 1015-1026
    Details
    In: Bulletin of the American Meteorological Society, American Meteorological Society, Vol. 99, No. 5 ( 2018-05), p. 1015-1026
    Abstract: While chaos ensures that probabilistic weather forecasts cannot always be “sharp,” it is important for users and developers that they are reliable. For example, they should not be overconfident or underconfident. The “spread–error” relationship is often used as a first-order assessment of the reliability of ensemble weather forecasts. This states that the ensemble standard deviation (a measure of forecast uncertainty) should match the root-mean-square error on the ensemble mean (when averaged over a sufficient number of forecast start dates). It is shown here that this relationship is now largely satisfied at the European Centre for Medium-Range Weather Forecasts (ECMWF) for ensemble forecasts of the midlatitude, midtropospheric flow out to lead times of at least 10 days when averaged over all flow situations throughout the year. This study proposes a practical framework for continued improvement in the reliability (and skill) of such forecasts. This involves the diagnosis of flow-dependent deficiencies in short-range (∼12 h) reliability for a range of synoptic-scale flow types and the prioritization of modeling research to address these deficiencies. The approach is demonstrated for a previously identified flow type, a trough over the Rockies with warm, moist air ahead. The mesoscale convective systems that can ensue are difficult to predict and, by perturbing the jet stream, are thought to lead to deterministic forecast “busts” for Europe several days later. The results here suggest that jet stream spread is insufficient during this flow type, and thus unreliable. This is likely to mean that the uncertain forecasts for Europe may, nevertheless, still be overconfident.
    Type of Medium: Online Resource
    ISSN: 0003-0007 , 1520-0477
    URL: Article
    DOI: 10.1175/BAMS-D-17-0027.1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2018
    detail.hit.zdb_id: 2029396-3
    detail.hit.zdb_id: 419957-1
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  • 5
    Online Resource
    Online Resource
    A New Framework for Identifying and Investigating Seasonal Climate Extremes
    American Meteorological Society ; 2021
    In:  Journal of Climate Vol. 34, No. 19 ( 2021-10), p. 7761-7782
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 34, No. 19 ( 2021-10), p. 7761-7782
    Abstract: Previous studies have recognized the societal relevance of climatic extremes on the seasonal time scale and examined physical processes leading to individual high-impact extreme seasons (e.g., extremely wet or warm seasons). However, these findings have not yet been generalized beyond case studies since at any specific location only very few seasonal events of such rarity occurred in the observational record. In this concept paper, a pragmatic approach to pool seasonal extremes across space is developed and applied to investigate hot summers and cold winters in ERA-Interim and the Community Earth System Model Large Ensemble (CESM-LENS). We identify spatial extreme season objects as contiguous regions of extreme seasonal mean temperatures based on statistical modeling. Regional pooling of extreme season objects in CESM-LENS then yields considerable samples of analogs to even the most extreme ERA-Interim events. This approach offers numerous opportunities for systematically analyzing large samples of extreme seasons, and several such analyses are illustrated. We reveal a striking co-occurrence of El Niño to La Niña transitions and the largest ERA-Interim midlatitude extreme summer events. Moreover, we perform a climate model evaluation with regard to extreme season size and intensity measures and estimate how often an extreme winter like the cold North American 2013/14 winter is expected anywhere in midlatitude regions. Furthermore, we present a large set of simulated analogs to this event, which makes it possible to study commonalities and differences of their underlying physical processes. Finally, substantial but spatially varying climatological differences in the size of extreme summer and extreme winter objects are identified.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    URL: Article
    DOI: 10.1175/JCLI-D-20-0953.1
    DOI: 10.1175/JCLI-D-20-0953.s1
    RVK:
    UA 4548
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2021
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 6
    Online Resource
    Online Resource
    Global Climatologies of Eulerian and Lagrangian Flow Features based on ERA-Interim
    American Meteorological Society ; 2017
    In:  Bulletin of the American Meteorological Society Vol. 98, No. 8 ( 2017-08-01), p. 1739-1748
    Details
    In: Bulletin of the American Meteorological Society, American Meteorological Society, Vol. 98, No. 8 ( 2017-08-01), p. 1739-1748
    Abstract: This paper introduces a newly compiled set of feature-based climatologies identified from ERA-Interim (1979–2014). Two categories of flow features are considered: (i) Eulerian climatologies of jet streams, tropopause folds, surface fronts, cyclones and anticyclones, blocks, and potential vorticity streamers and cutoffs and (ii) Lagrangian climatologies, based on a large ensemble of air parcel trajectories, of stratosphere–troposphere exchange, warm conveyor belts, and tropical moisture exports. Monthly means of these feature climatologies are openly available at the ETH Zürich web page (http://eraiclim.ethz.ch) and are annually updated. Datasets at higher resolution can be obtained from the authors on request. These feature climatologies allow studying the frequency, variability, and trend of atmospheric phenomena and their interrelationships across temporal scales. To illustrate the potential of this dataset, boreal winter climatologies of selected features are presented and, as a first application, the very unusual Northern Hemispheric winter of 2009/10 is identified as the season when most of the considered features show maximum deviations from climatology. The second application considers dry winters in the western United States and reveals fairly localized anomalies in the eastern North Pacific of enhanced blocking and surface anticyclones and reduced cyclones.
    Type of Medium: Online Resource
    ISSN: 0003-0007 , 1520-0477
    URL: Article
    URL: Article
    DOI: 10.1175/BAMS-D-15-00299.1
    DOI: 10.1175/BAMS-D-15-00299.2
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2017
    detail.hit.zdb_id: 2029396-3
    detail.hit.zdb_id: 419957-1
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  • 7
    Online Resource
    Online Resource
    Northern Hemisphere Extratropical Cyclones: A Comparison of Detection and Tracking Methods and Different Reanalyses
    American Meteorological Society ; 2008
    In:  Monthly Weather Review Vol. 136, No. 3 ( 2008-03-01), p. 880-897
    Details
    In: Monthly Weather Review, American Meteorological Society, Vol. 136, No. 3 ( 2008-03-01), p. 880-897
    Abstract: The applicability of three different cyclone detection and tracking schemes is investigated with reanalysis datasets. First, cyclone climatologies and cyclone characteristics of the 40-yr ECMWF Re-Analysis (ERA-40) are compared with the NCEP–NCAR dataset using one method. ERA-40 shows systematically more cyclones, and therefore a higher cyclone center density, than the NCEP–NCAR reanalysis dataset. Geostrophically adjusted geopotential height gradients around cyclone centers, a measure of cyclone intensity, are enhanced in ERA-40 compared with the NCEP–NCAR reanalysis dataset. The variability of the number of cyclones per season is significantly correlated between the two reanalysis datasets, but time series of the extreme cyclone intensity exhibit a higher correlation. This suggests that the cyclone intensity is a more robust measure of variability than the number of cyclones. Second, three cyclone detection and tracking schemes are compared, based on the ERA-40 dataset. In general the schemes show a good correspondence. The approaches differ in technical aspects associated with the cyclone identification and the tracking procedure, leading to deviations in cyclone track length. However, it is often not clear which scheme is correct or incorrect. With the application of lifetime thresholds, some of the cyclone tracks are too short to be included in statistical measures of cyclones. Nevertheless, consequences of these differences in mean cyclone characteristics are minor, but for specific research questions—for example, what is the cyclone activity in the Mediterranean in winter—the users should be aware of these potential differences and adjust their scheme if necessary. A trend analysis of cyclone characteristics shows that results appear to be sensitive to both the choice of cyclone detection and tracking schemes and the reanalysis dataset.
    Type of Medium: Online Resource
    ISSN: 1520-0493 , 0027-0644
    URL: Article
    DOI: 10.1175/2007MWR2143.1
    RVK:
    RA 1000
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2008
    detail.hit.zdb_id: 2033056-X
    detail.hit.zdb_id: 202616-8
    SSG: 14
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  • 8
    Online Resource
    Online Resource
    The North Atlantic Waveguide and Downstream Impact Experiment
    American Meteorological Society ; 2018
    In:  Bulletin of the American Meteorological Society Vol. 99, No. 8 ( 2018-08), p. 1607-1637
    Details
    In: Bulletin of the American Meteorological Society, American Meteorological Society, Vol. 99, No. 8 ( 2018-08), p. 1607-1637
    Abstract: The North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX) explored the impact of diabatic processes on disturbances of the jet stream and their influence on downstream high-impact weather through the deployment of four research aircraft, each with a sophisticated set of remote sensing and in situ instruments, and coordinated with a suite of ground-based measurements. A total of 49 research flights were performed, including, for the first time, coordinated flights of the four aircraft: the German High Altitude and Long Range Research Aircraft (HALO), the Deutsches Zentrum für Luft- und Raumfahrt (DLR) Dassault Falcon 20, the French Service des Avions Français Instrumentés pour la Recherche en Environnement (SAFIRE) Falcon 20, and the British Facility for Airborne Atmospheric Measurements (FAAM) BAe 146. The observation period from 17 September to 22 October 2016 with frequently occurring extratropical and tropical cyclones was ideal for investigating midlatitude weather over the North Atlantic. NAWDEX featured three sequences of upstream triggers of waveguide disturbances, as well as their dynamic interaction with the jet stream, subsequent development, and eventual downstream weather impact on Europe. Examples are presented to highlight the wealth of phenomena that were sampled, the comprehensive coverage, and the multifaceted nature of the measurements. This unique dataset forms the basis for future case studies and detailed evaluations of weather and climate predictions to improve our understanding of diabatic influences on Rossby waves and the downstream impacts of weather systems affecting Europe.
    Type of Medium: Online Resource
    ISSN: 0003-0007 , 1520-0477
    URL: Article
    DOI: 10.1175/BAMS-D-17-0003.1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2018
    detail.hit.zdb_id: 2029396-3
    detail.hit.zdb_id: 419957-1
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