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  • 1995-1999  (10)
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Keywords
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Simulations of stratospheric sudden warmings in the Berlin troposphere-stratosphere-mesosphere GCM (1996)
    Springer
    Annales geophysicae 14 (1996), S. 443-463 
    Details
    ISSN: 0992-7689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Stratospheric sudden warming events in the Northern Hemisphere of the Berlin TSM GCM are investigated. In about 50% of the simulated years (13 out of 28), major midwinter warmings occur. This agrees well with observations but, whereas real events tend to occur approximately every second season, those in the model are clustered, most of them occur in the period between years 15/16 and years 24/25. In most other years, minor warming events take place. The warming events are found earlier in the winter than in reality. Many of the observed characteristics of warming events are well captured by the model: pulses of wave activity propagate out of the troposphere; these transient events force the zonal-mean zonal wind in the stratosphere and coincide with increases of the temperature at the North Pole and cooling at low levels in the tropics; temperature changes of opposite sign are modelled at higher levels. Synoptically, the modelled stratosphere evolves quite realistically before the warmings: the cyclonic vortex is displaced from the Pole by an amplifying anticyclone. After minor warmings, the stratosphere remains too disturbed as the cyclonic centre does not return to the North Pole as quickly as in reality. In the aftermath of major warmings the cyclonic vortex is not fully eroded and the anticyclonic circulation does not develop properly over the Pole; furthermore, the wintertime circulation is not properly restored after the event.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-996-0443-6
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    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    A comparison of reanalyses in the tropical stratosphere. Part 3: inclusion of the pre-satellite data era (1999)
    Springer
    Climate dynamics 15 (1999), S. 241-250 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract  In this study, previous evaluations of the monthly mean structure of the tropical lower stratosphere in reanalyzed datasets are extended to include the period 1958–1978, when no satellite-based observations were available. It is shown that a large discontinuity, in temperatures near the tropical tropopause, in the NCEP data occurred when the Tiros Operational Vertical Sounder (TOVS) became operational. When only rawinsonde data were available, the tropopause temperatures in the NCEP dataset are in better agreement with ERA data for TOVS period. Both NCEP and NASA reanalyses show similar deviations from the ERA data in the TOVS renalyses show similar deviations from the ERA data in the TOVS period. There is also a stepwise change in the lower stratospheric meridional velocity when the TOVS data were introduced into the NCEP reanalyses. This discontinuity is such that in the 1958–1978 period, the annual cycle in zonal mean meridional velocity in the NCEP data resembles that of the ERA data in the 1979–1993 period. The differences are shown to result from large changes in the local meridional flow in the Indonesian region. The temporal consistency of the QBO is examined; it is shown that the NCEP assimilation system is sensitive to the data available. There is a change in the zonally asymmetric structure of the zonal wind over time, presumably related to the changes in input data and the inability of the model to represent the three-dimensional structure of the tropical lower stratosphere. These results provide further evidence of the value of rawinsonde data in data assimilation systems as well as the need to use satellite radiance data in an appropriate manner.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820050279
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    A comparison of reanalyses in the tropical stratosphere. Part 1: thermal structure and the annual cycle (1998)
    Springer
    Climate dynamics 14 (1998), S. 631-644 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract  An intercomparison of the thermal structure and the annual cycle in the tropical lower stratosphere of two reanalysis datasets is presented. These are from the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) and the European Centre for Medium Range Weather Forecasts (ECMWF Re-Analysis: ERA). Generally, the ERA data are coldest and in better agreement with radiosonde observations; this is particularly apparent at 100 hPa where there is also a strong geographic bias, the maximum differences (more than 4 K) occurring over the southern Pacific and the Indian Ocean, with much smaller (sometimes reversed) differences over land. The NCEP temperatures are biased towards satellite-derived values, while the ERA data resolve the low tropopause temperatures much better. The lower ERA temperatures have important implications for the cross-tropopause exchange of water vapor. The meridional-height structure of the annual cycles agree quite well, but the amplitude in the ERA data is about 50% stronger than in NCEP at 70 hPa (in better agreement with previous studies) and weaker at lower pressures. As in previous studies, an anticorrelation is found between the tropical and extratropical temperatures of the reanalyses. The mean meridional flow at the equator is northward all year at all stratospheric levels in the NCEP data, implying a mass transport from the Southern to the Northern Hemisphere; in the ERA data the expected annual cycle (flow from summer to winter) is reproduced with very small annual mean exchange.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820050246
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    A comparison of reanalyses in the tropical stratosphere. Part 2: the quasi-biennial oscillation (1998)
    Springer
    Climate dynamics 14 (1998), S. 645-658 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract  Reanalysis datasets potentially offer the opportunity to examine the tropical quasi-biennial oscillation (QBO) in greater detail than in the past, including the associated meridional circulation and the links with other parts of the atmosphere. For such studies to be useful, the QBO represented by the reanalyses should be realistic. In this work, the QBO in the ERA and NCEP reanalyses is validated against rawinsonde observations from Singapore. Monthly mean data are used. In the lower stratosphere (at 50 hPa and 30 hPa) the ERA QBO is reasonable, although the wind extrema in both phases are too weak and the vertical shear and the temperature anomalies are too small. The NCEP QBO is weaker still. At 10 hPa neither reanalysis system performs well, both systems failing to reproduce the westerlies, possibly because of the proximity of the upper boundary. The Singapore wind is representative of the zonal means in the reanalyses. The weak wind extrema in the reanalyses would not support a wave-mean flow interaction theory of the QBO, because a large portion of the gravity wave spectrum which would be absorbed in reality would be transmitted beyond 10 hPa. The stronger shear zones captured in the ERA data are associated with larger, more realistic temperature perturbations near 30 hPa. The northward velocities in the NCEP data show a more realistic structure than in the ERA reanalysis, where they are dominated by a vertical “gridpoint wave” structure in the lowermost stratosphere. Despite the shortcomings of the reanalyses, the high correlations of the wind at 30 hPa and 50 hPa with the observations at Singapore mean that the reanalyses could potentially be used to examine the effects of the QBO away from the tropical stratosphere. Future reanalyses need to take full account of the wind shears evident in the rawinsonde observations and use models with an adequate resolution to capture these vertical scales.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820050247
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    Paper (German National Licenses)
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  • 5
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    Uses of satellite observations to validate climate/middle atmosphere models (1998)
    Elsevier
    Details
    Publication Date: 1998-01-01
    Print ISSN: 0273-1177
    Electronic ISSN: 1879-1948
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Elsevier
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  • 6
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    Simulations of stratospheric sudden warmings in the Berlin troposphere-stratosphere-mesosphere GCM (1996)
    Copernicus
    Details
    Publication Date: 1996-04-30
    Description: Stratospheric sudden warming events in the Northern Hemisphere of the Berlin TSM GCM are investigated. In about 50% of the simulated years (13 out of 28), major midwinter warmings occur. This agrees well with observations but, whereas real events tend to occur approximately every second season, those in the model are clustered, most of them occur in the period between years 15/16 and years 24/25. In most other years, minor warming events take place. The warming events are found earlier in the winter than in reality. Many of the observed characteristics of warming events are well captured by the model: pulses of wave activity propagate out of the troposphere; these transient events force the zonal-mean zonal wind in the stratosphere and coincide with increases of the temperature at the North Pole and cooling at low levels in the tropics; temperature changes of opposite sign are modelled at higher levels. Synoptically, the modelled stratosphere evolves quite realistically before the warmings: the cyclonic vortex is displaced from the Pole by an amplifying anticyclone. After minor warmings, the stratosphere remains too disturbed as the cyclonic centre does not return to the North Pole as quickly as in reality. In the aftermath of major warmings the cyclonic vortex is not fully eroded and the anticyclonic circulation does not develop properly over the Pole; furthermore, the wintertime circulation is not properly restored after the event.
    Print ISSN: 0992-7689
    Electronic ISSN: 1432-0576
    Topics: Geosciences , Physics
    Published by Copernicus on behalf of European Geosciences Union.
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  • 7
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    A comparison of reanalyses in the tropical stratosphere. Part 2: the quasi-biennial oscillation (1998)
    Springer
    Details
    Publication Date: 1998-07-29
    Print ISSN: 0930-7575
    Electronic ISSN: 1432-0894
    Topics: Geosciences , Physics
    Published by Springer
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  • 8
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    A comparison of reanalyses in the tropical stratosphere. Part 3: inclusion of the pre-satellite data era (1999)
    Springer
    Details
    Publication Date: 1999-04-07
    Print ISSN: 0930-7575
    Electronic ISSN: 1432-0894
    Topics: Geosciences , Physics
    Published by Springer
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  • 9
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    A comparison of reanalyses in the tropical stratosphere. Part 1: thermal structure and the annual cycle (1998)
    Springer
    Details
    Publication Date: 1998-07-29
    Print ISSN: 0930-7575
    Electronic ISSN: 1432-0894
    Topics: Geosciences , Physics
    Published by Springer
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  • 10
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    The Tropical Upper Troposphere and Lower Stratosphere in the GEOS-2 GCM (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: The structure of the tropical upper troposphere and lower stratosphere in the GEOS-2 General Circulation Model (GCM) is discussed. The emphasis of this study is on the reality of monthly-mean temperature and water vapor distributions in the model, compared to reasonable observational estimates. It is shown that although the zonal-mean temperature is in good agreement with observations, the GCM supports an excessive zonal asymmetry near the tropopause compared to the ECMWF Reanalyses. In reality there is a QBO-related variability in the zonally averaged lower stratospheric temperature which is not captured by the model. The observed upper tropospheric temperature and humidity fields show variations related to those in the sea surface temperature, which are not incorporated in the GCM; nevertheless, there is some interannual variability in the GCM, indicating a component arising from internal processes. The model is too moist in the middle troposphere (500 hPa) but too dry in the upper troposphere, suggesting that there is too little vertical transport or too much drying in the GCM. Transport into the stratosphere shows a pronounced annual cycle, with drier air entering the tropical stratosphere when the tropopause is coldest in northern winter; while the alternating dry and moist air masses can be traced ascending through the tropical lower stratosphere, the progression of the anomalies is too rapid.
    Keywords: Geophysics
    Format: application/pdf
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