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  • 1
    Publication Date: 2023-06-22
    Description: We present a partition-enhanced least-squares collocation (PE-LSC) which comprises several modifications to the classical LSC method. It is our goal to circumvent various problems of the practical application of LSC. While these investigations are focused on the modeling of the exterior gravity field the elaborated methods can also be used in other applications. One of the main drawbacks and current limitations of LSC is its high computational cost which grows cubically with the number of observation points. A common way to mitigate this problem is to tile the target area into sub-regions and solve each tile individually. This procedure assumes a certain locality of the LSC kernel functions which is generally not given and, therefore, results in fringe effects. To avoid this, it is proposed to localize the LSC kernels such that locality is preserved, and the estimated variances are not notably increased in comparison with the classical LSC method. Using global covariance models involves the calculation of a large number of Legendre polynomials which is usually a time-consuming task. Hence, to accelerate the creation of the covariance matrices, as an intermediate step we pre-calculate the covariance function on a two-dimensional grid of isotropic coordinates. Based on this grid, and under the assumption that the covariances are sufficiently smooth, the final covariance matrices are then obtained by a simple and fast interpolation algorithm. Applying the generalized multi-variate chain rule, also cross-covariance matrices among arbitrary linear spherical harmonic functionals can be obtained by this technique. Together with some further minor alterations these modifications are implemented in the PE-LSC method. The new PE-LSC is tested using selected data sets in Antarctica where altogether more than 800,000 observations are available for processing. In this case, PE-LSC yields a speed-up of computation time by a factor of about 55 (i.e., the computation needs only hours instead of weeks) in comparison with the classical unpartitioned LSC. Likewise, the memory requirement is reduced by a factor of about 360 (i.e., allocating memory in the order of GB instead of TB).
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Technische Universität München (1025)
    Keywords: ddc:526 ; Gravity field ; Least squares collocation (LSC) ; Covariance function ; Data combination ; Prediction ; Antarctica
    Language: English
    Type: doc-type:article
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  • 2
    Publication Date: 2021-09-21
    Description: Simulation characteristics from eighteen global ocean–sea-ice coupled models are presented with a focus on the mean Atlantic meridional overturning circulation (AMOC) and other related fields in the North Atlantic. These experiments use inter-annually varying atmospheric forcing data sets for the 60- 1 Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site year period from 1948 to 2007 and are performed as contributions to the second phase of the Coordinated Ocean-ice Reference Experiments (CORE-II). The protocol for conducting such CORE-II experiments is summarized. Despite using the same atmospheric forcing, the solutions show significant differences. As most models also differ from available observations, biases in the Labrador Sea region in upper-ocean potential temperature and salinity distributions, mixed layer depths, and sea-ice cover are identified as contributors to differences in AMOC. These differences in the solutions do not suggest an obvious grouping of the models based on their ocean model lineage, their vertical coordinate representations, or surface salinity restoring strengths. Thus, the solution differences among the models are attributed primarily to use of different subgrid scale parameterizations and parameter choices as well as to differences in vertical and horizontal grid resolutions in the ocean models. Use of a wide variety of sea-ice models with diverse snow and sea-ice albedo treatments also contributes to these differences. Based on the diagnostics considered, the majority of the models appear suitable for use in studies involving the North Atlantic, but some models require dedicated development effort.
    Description: U.S. National Science Foundation (NSF) NSF U.S. Department of Energy NOAA Climate Program Office under Climate Variability Predictability Program NA09OAR4310163 Department of Climate Change and Energy Efficiency Bureau of Meteorology CSIRO National Computational Infrastructure facility at the Australian National University Research Council of Norway through the EarthClim 207711/E10 NOTUR/NorStore projects Centre for Climate Dynamics at the Bjerknes Centre for Climate Research Italian Ministry of Education, University, and Research Italian Ministry of Environment, Land, and Sea under the GEMINA project BNP-Paribas foundation via the PRECLIDE project under the CNRS 30023488 WGOMD
    Description: Published
    Description: 76-107
    Description: 4A. Clima e Oceani
    Description: JCR Journal
    Description: open
    Keywords: Global ocean–sea-ice modelling ; Ocean model comparisons ; Atmospheric forcing ; Experimental design ; Atlantic meridional overturning circulation ; North Atlantic simulations ; 03. Hydrosphere::03.03. Physical::03.03.03. Interannual-to-decadal ocean variability
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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