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  • Wiley  (3)
  • IEEE  (2)
  • AWI Computing and Data Centre  (1)
  • 1
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    AWI Computing and Data Centre
    In:  EPIC3Second Data Science Symposium, Bremerhaven, Auditorium Nordseemuseum, 2018-12-06-2018-12-06Bremerhaven, AWI Computing and Data Centre
    Publication Date: 2020-03-16
    Description: The second Data Science Symposium at AWI gathered several data science related talks from AWI, GEOMAR and HZG.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
    Format: application/pdf
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  • 2
    Publication Date: 2021-02-08
    Description: Antarctic Intermediate Water (AAIW) is an important conduit for nutrients to reach the nutrient‐poor low‐latitude ocean areas. In the Atlantic, it forms part of the return path of the Atlantic Meridional Overturning Circulation (AMOC). Despite the importance of AAIW, little is known about variations in its composition and signature during the prominent AMOC and climate changes of the last deglaciation. Here, we reconstruct benthic foraminiferal Mg/Ca‐based intermediate water temperatures (IWTMg/Ca) and intermediate water neodymium (Nd) isotope compositions at sub‐millennial resolution from unique sediment cores located at the northern tip of modern AAIW extent in the tropical W‐Atlantic (850 and 1018 m water depth). Our data indicate a pronounced warming of AAIW in the tropical W‐Atlantic during Heinrich Stadial 1 (HS1) and the Younger Dryas (YD). We argue that these warming events were induced by major AMOC perturbations resulting in the pronounced accumulation of heat in the surface Southern Ocean. Combined with published results, our data suggest the subsequent uptake of Southern Ocean heat by AAIW and its rapid northward transfer to the tropical W‐Atlantic. Hence, the rapid deglacial northern climate perturbations directly controlled the AAIW heat budget in the tropical W‐Atlantic after a detour via the Southern Ocean. We speculate that the ocean heat redistribution via AAIW effectively dampened Southern Hemisphere warming during the deglaciation and may therefore have been a crucial player in the climate seesaw mechanisms between the two hemispheres.
    Type: Article , PeerReviewed
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  • 3
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    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 118 . pp. 2761-2773.
    Publication Date: 2018-02-27
    Description: A realistic primitive-equation model of the Southern Ocean at eddying spatial resolution is used to examine the effect of ocean-surface-velocity dependence of the wind stress on the strength of near-inertial oscillations. Accounting for the ocean-surface-velocity dependence of the wind stress leads to a large reduction of wind-induced near-inertial energy of approximately 40 percent and of wind power input into the near-inertial frequency band of approximately 20 percent. A large part of this reduction can be explained by the leading-order modification to the wind stress if the ocean-surface velocity is included. The strength of the reduction is shown to be modulated by the inverse of the ocean-surface-mixed-layer depth. We conclude that the effect of surface-velocity dependence of the wind stress should be taken into account when estimating the wind-power input into the near-inertial frequency band and when estimating near-inertial energy levels in the ocean due to wind forcing.
    Type: Article , PeerReviewed
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  • 4
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    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Oceans, 119 (1). pp. 359-376.
    Publication Date: 2019-09-23
    Description: We use an eddying realistic primitive equation model of the Southern Ocean to examine the spatial and temporal distribution of near-inertial wind-power input (WPI) and near-inertial energy (NIE) in the Southern Ocean. We find that the modelled near-inertial WPI is almost proportional to inertial wind-stress variance (IWSV), while the modelled NIE is modulated by the inverse of the mixed-layer depth. We go on to assess recent decadal trends of near-inertial WPI from trends of IWSV based on reanalysis wind-stress. Averaged over the Southern Ocean, annual-mean IWSV is found to have increased by 16 percent over the years 1979 through 2011. Part of the increase of IWSV is found to be related to the positive trend of the Southern Annular Mode over the same period. Finally, we show that there are horizontal local maxima of NIE at depth that are almost exclusively associated with anticyclonic eddies.
    Type: Article , PeerReviewed
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  • 5
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    IEEE
    In:  [Paper] In: 2021 IEEE/ACM 6th International Workshop on Metamorphic Testing (MET), 22.-30.05.2021, Virtual (originally Madrid, Spain) . Proceedings from IEEE/ACM International Workshop on Metamorphic Testing (MET) ; pp. 42-46 .
    Publication Date: 2021-08-10
    Description: Metamorphic testing seeks to verify software in the absence of test oracles. Our application domain is ocean system modeling, where test oracles rarely exist, but where symmetries of the simulated physical systems are known. The input data set is large owing to the requirements of the application domain.This paper presents work in progress for the automated generation of metamorphic test scenarios using machine learning. We extended our previously proposed method [1] to identify metamorphic relations with reduced computational complexity. Initially, we represent metamorphic relations as identity maps. We construct a cost function that minimizes for identifying a metamorphic relation orthogonal to previously found metamorphic relations and penalize for the identity map. A machine learning algorithm is used to identify all possible metamorphic relations minimizing the defined cost function. We propose applying dimensionality reduction techniques to identify attributes in the input which have high variance among the identified metamorphic relations. We apply mutation on these selected attributes to identify distinct metamorphic relations with reduced computational complexity. For experimental evaluation, we subject the two implementations of an ocean-modeling application to the proposed method to present the use of metamorphic relations to test the two implementations of this application.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 6
    Publication Date: 2023-11-01
    Description: Working with observational data in the context of geophysics can be challenging, since we often have to deal with missing data. This requires imputation techniques in pre-processing to obtain data-mining-ready samples. Here, we present a convolutional neural network approach from the domain of deep learning to reconstruct complete information from sparse inputs. As data, we use various two-dimensional geospatial fields. To have consistent data over a sufficiently long time span, we favor to work with output from control simulations of two Earth System Models, namely the Flexible Ocean and Climate Infrastructure and the Community Earth System Model. Our networks can restore complete information from incomplete input samples with varying rates of missing data. Moreover, we apply a bottom-up sampling strategy to identify the most relevant grid points for each input feature. Choosing the optimal subset of grid points allows us to successfully reconstruct current fields and to predict future fields from ultra sparse inputs. As a proof of concept, we predict El Niño Southern Oscillation and rainfall in the African Sahel region from sea surface temperature and precipitation data, respectively. To quantify uncertainty, we compare corresponding climate indices derived from reconstructed versus complete fields.
    Type: Conference or Workshop Item , NonPeerReviewed
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