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  • 1
    Publication Date: 2019-02-01
    Description: The parameterization of sub-grid scale processes is one of the key challenges towards improved numerical simulations of the atmospheric and oceanic circulation. Numerical weather prediction models as well as climate models would benefit from more sophisticated turbulence closures that allow for less spurious dissipation at the grid-scale and consequently higher and more realistic levels of eddy kinetic energy (EKE). Recent studies propose to use a hyperviscous closure in combination with an additional deterministic forcing term as a negative viscosity to represent backscatter of energy from unresolved scales. The sub-grid EKE is introduced as an additional prognostic variable that is fed by dissipation at the grid scale, and enables recycling of EKE via the backscatter term at larger scales. This parameterization was previously shown to work well in zonally re-entrant channel configurations. Here, a generalization in the form of a Rossby number-dependent scaling for the strength of the backscatter is introduced to represent the emergence of a forward energy-cascade in unbalanced flows near the boundaries. We apply the parameterization to a shallow water model of a double gyre basin and provide evidence for its general applicability. In terms of mean state and variability, a low resolution model is considerably improved towards a high resolution control run at low additional computational cost.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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  • 2
    Publication Date: 2018-06-19
    Description: For more than a decade meteorologists at the German Antarctic research station Neumayer (70°S, 008°W) offer detailed and individual summer weather forecasts for all activities in the Dronning Maud Land. Especially the intercontinental air link with Cape Town made the establishment of this service mandatory. The work is performed in close cooperation between the Alfred Wegener Institute for Polar and Marine Research (AWI) and the German Weather Service (DWD). The forecasts base mainly on in situ data including automatic weather stations (AWS), on near real time satellite pictures and on a variety of model products mainly from the Antarctic Mesoscale Prediction System (AMPS) and the European Centre for Medium-Range Weather Forecasts (ECMWF). To optimize this service the errors of a typical AWS had been quantified by running an unmaintained AWS one year side by side of the maintained instruments from the meteorological observatory from Neumayer. In a second year the same AWS was placed 11 km north of Neumayer to judge the spatial footprint of the observatory data. By comparing model products with the measurements of the observatory systematic errors in the forecast products have been observed. Also the ERA-Interim reanalysis differs significantly from the temperature time series observed at Neumayer despite the fact that the data is fed into the Global Telecommunication System GTS for more than 30 years. From these findings some guidance on optimizing the Antarctic observing and prediction systems could be developed.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 3
    Publication Date: 2017-03-06
    Description: Highlights: • North Atlantic sea surface temperature exhibits high decadal predictability potential. • Model bias hinders exploiting the decadal predictability potential. • An innovative method was developed to overcome some of the bias problem. • North Atlantic sea surface temperature will stay anomalously warm until about 2030. Abstract: The Atlantic Meridional Overturning Circulation (AMOC), a major current system in the Atlantic Ocean, is thought to be an important driver of climate variability, both regionally and globally and on a large range of time scales from decadal to centennial and even longer. Measurements to monitor the AMOC strength have only started in 2004, which is too short to investigate its link to long-term climate variability. Here the surface heat flux-driven part of the AMOC during 1900–2010 is reconstructed from the history of the North Atlantic Oscillation, the most energetic mode of internal atmospheric variability in the Atlantic sector. The decadal variations of the AMOC obtained in that way are shown to precede the observed decadal variations in basin-wide North Atlantic sea surface temperature (SST), known as the Atlantic Multidecadal Oscillation (AMO) which strongly impacts societally important quantities such as Atlantic hurricane activity and Sahel rainfall. The future evolution of the AMO is forecast using the AMOC reconstructed up to 2010. The present warm phase of the AMO is predicted to continue until the end of the next decade, but with a negative tendency.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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  • 4
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    In:  [Talk] In: Ocean Sciences Meeting 2014, 23.-28.02.2014, Honululu, Hawaii, USA .
    Publication Date: 2015-01-15
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 5
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    In:  (Bachelor thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 53 pp
    Publication Date: 2015-03-17
    Type: Thesis , NonPeerReviewed
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  • 6
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    In:  (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 92 pp
    Publication Date: 2018-01-10
    Keywords: Course of study: MSc Climate Physics
    Type: Thesis , NonPeerReviewed
    Format: text
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  • 7
    Publication Date: 2015-01-15
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 8
    Publication Date: 2014-09-25
    Description: For more than a decade meteorologists at the German Antarctic research station Neumayer (70°S, 008°W) offer detailed and individual summer weather forecasts for all activities in the Dronning Maud Land. Especially the intercontinental air link with Cape Town made the establishment of this service mandatory. The work is performed in close cooperation between the Alfred Wegener Institute for Polar and Marine Research (AWI) and the German Weather Service (DWD). The forecasts base mainly on in situ data including automatic weather stations (AWS), on near real time satellite pictures and on a variety of model products mainly from the Antarctic Mesoscale Prediction System (AMPS) and the European Centre for Medium-Range Weather Forecasts (ECMWF). To optimize this service the errors of a typical AWS had been quantified by running an unmaintained AWS one year side by side of the maintained instruments from the meteorological observatory from Neumayer. In a second year the same AWS was placed 11 km north of Neumayer to judge the spatial footprint of the observatory data. By comparing model products with the measurements of the observatory systematic errors in the forecast products have been observed. Also the ERA-Interim reanalysis differs significantly from the temperature time series observed at Neumayer despite the fact that the data is fed into the Global Telecommunication System GTS for more than 30 years. From these findings some guidance on optimizing the Antarctic observing and prediction systems could be developed.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 9
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    PANGAEA
    In:  Supplement to: Klöwer, Milan; Jung, Thomas; König-Langlo, Gert; Semmler, Tido (2013): Aspects of weather parameters at Neumayer station, Antarctica, and their representation in reanalysis and climate model data. Meteorologische Zeitschrift, 22(6), 699-709, https://doi.org/10.1127/0941-2948/2013/0505
    Publication Date: 2019-05-15
    Description: ERA-Interim reanalysis data and data of the Hadley Centre Global Environmental Model version 2 (HadGEM2) are compared with continuous meteorological observations of near-surface wind and temperature carried out for more than 30 years at Neumayer station, situated on the Ekstro¨m Ice Shelf of Antarctica. Significant temperature correlations between Neumayer climate and the climate of both the interior of the Antarctic continent and oceanic regions north of Neumayer are investigated using observational data and model data. Mean sea level pressure fluctuations at Neumayer can be connected to changes in the Southern Annular Mode (SAM). Shortcomings in the ERA-Interim reanalysis data with spurious trends of up to 7 C over 31 years are identified at several places in Antarctica. Furthermore, it is shown that katabatic winds in both the ERA-Interim reanalysis data and in the HadGEM2 climate model are underrepresented in frequency and speed, presumably due to the problems in representing topography in these relatively coarse resolution models. This may be one reason for the positive 2m air temperature bias of 3 C in the models at Neumayer station. The results of this study reemphasize that climatic trends in regions with a low station density can not be assessed solely from model data. Thus, it is absolutely necessary to maintain polar observatories such as Neumayer station to quantify climate change over the Southern Ocean and Antarctica.
    Type: Dataset
    Format: text/tab-separated-values, 1488 data points
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  • 10
    Publication Date: 2019-07-17
    Description: ERA-Interim reanalysis data and data of the Hadley Centre Global Environmental Model version 2 (HadGEM2) are compared with continuous meteorological observations of near-surface wind and temperature carried out for more than 30 years at Neumayer station, situated on the Ekström Ice Shelf of Antarctica. Significant temperature correlations between Neumayer climate and the climate of both the interior of the Antarctic continent and oceanic regions north of Neumayer are investigated using observational data and model data. Mean sea level pressure fluctuations at Neumayer can be connected to changes in the Southern Annular Mode (SAM). Shortcomings in the ERA-Interim reanalysis data with spurious trends of up to 7 °C over 31 years are identified at several places in Antarctica. Furthermore, it is shown that katabatic winds in both the ERA-Interim reanalysis data and in the HadGEM2 climate model are underrepresented in frequency and speed, presumably due to the problems in representing topography in these relatively coarse resolution models. This may be one reason for the positive 2m air temperature bias of 3 °C in the models at Neumayer station. The results of this study reemphasize that climatic trends in regions with a low station density can not be assessed solely from model data. Thus, it is absolutely necessary to maintain polar observatories such as Neumayer station to quantify climate change over the Southern Ocean and Antarctica.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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