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  • MDPI AG  (4)
  • 2020-2024  (4)
  • 1
    Online Resource
    Online Resource
    Internal Model Variability of the Regional Coupled System Model GCOAST-AHOI
    MDPI AG ; 2020
    In:  Atmosphere Vol. 11, No. 3 ( 2020-02-26), p. 227-
    Details
    In: Atmosphere, MDPI AG, Vol. 11, No. 3 ( 2020-02-26), p. 227-
    Abstract: Simulations of a Regional Climate Model (RCM) driven by identical lateral boundary conditions but initialized at different times exhibit the phenomenon of so-called internal model variability (or in short, Internal Variability—IV), which is defined as the inter-member spread between members in an ensemble of simulations. Our study investigates the effects of air-sea coupling on IV of the regional atmospheric model COSMO-CLM (CCLM) of the new regional coupled system model GCOAST-AHOI (Geesthacht Coupled cOAstal model SysTem: Atmosphere, Hydrology, Ocean and Sea Ice). We specifically address physical processes parameterized in CCLM, which may cause a large IV during an extreme event, and where this IV is affected by the air-sea coupling. Two six-member ensemble simulations were conducted with GCOAST-AHOI and the stand-alone CCLM (CCLM_ctr) for a period of 1 September–31 December 2013 over Europe. IV is expressed by spreads within the two sets of ensembles. Analyses focus on specific events during this period, especially on the storm Christian occurring from 27 to 29 October 2013 in northern Europe. Results show that simulations of CCLM_ctr vary largely amongst ensemble members during the storm. By analyzing two members of CCLM_ctr with opposite behaviors, we found that the large uncertainty in CCLM_ctr is caused by a combination of two factors (1) uncertainty in parameterization of cloud-radiation interaction in the atmospheric model. and (2) lack of an active two-way air-sea interaction. When CCLM is two-way coupled with the ocean model, the ensemble means of GCOAST-AHOI and CCLM_ctr are relatively similar, but the spread is reduced remarkably in GCOAST-AHOI, not only over the ocean where the coupling is done but also over land due to the land-sea interactions.
    Type of Medium: Online Resource
    ISSN: 2073-4433
    URL: Article
    DOI: 10.3390/atmos11030227
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
    detail.hit.zdb_id: 2605928-9
    SSG: 23
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  • 2
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    Online Resource
    Effects of Wave-Induced Processes in a Coupled Wave–Ocean Model on Particle Transport Simulations
    MDPI AG ; 2021
    In:  Water Vol. 13, No. 4 ( 2021-02-05), p. 415-
    Details
    In: Water, MDPI AG, Vol. 13, No. 4 ( 2021-02-05), p. 415-
    Abstract: This study investigates the effects of wind–wave processes in a coupled wave–ocean circulation model on Lagrangian transport simulations. Drifters deployed in the southern North Sea from May to June 2015 are used. The Eulerian currents are obtained by simulation from the coupled circulation model (NEMO) and the wave model (WAM), as well as a stand-alone NEMO circulation model. The wave–current interaction processes are the momentum and energy sea state dependent fluxes, wave-induced mixing and Stokes–Coriolis forcing. The Lagrangian transport model sensitivity to these wave-induced processes in NEMO is quantified using a particle drift model. Wind waves act as a reservoir for energy and momentum. In the coupled wave–ocean circulation model, the momentum that is transferred into the ocean model is considered as a fraction of the total flux that goes directly to the currents plus the momentum lost from wave dissipation. Additional sensitivity studies are performed to assess the potential contribution of windage on the Lagrangian model performance. Wave-induced drift is found to significantly affect the particle transport in the upper ocean. The skill of particle transport simulations depends on wave–ocean circulation interaction processes. The model simulations were assessed using drifter and high-frequency (HF) radar observations. The analysis of the model reveals that Eulerian currents produced by introducing wave-induced parameterization into the ocean model are essential for improving particle transport simulations. The results show that coupled wave–circulation models may improve transport simulations of marine litter, oil spills, larval drift or transport of biological materials.
    Type of Medium: Online Resource
    ISSN: 2073-4441
    URL: Article
    DOI: 10.3390/w13040415
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2521238-2
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  • 3
    Online Resource
    Online Resource
    Hydrodynamic Impacts on the Fate of Polychlorinated Biphenyl 153 in the Marine Environment
    MDPI AG ; 2022
    In:  Water Vol. 14, No. 23 ( 2022-12-05), p. 3952-
    Details
    In: Water, MDPI AG, Vol. 14, No. 23 ( 2022-12-05), p. 3952-
    Abstract: Due to their long half-life, polychlorinated biphenyls (PCBs) tend to contaminate not only coastal areas, but they travel over long distances, eventually reaching remote areas such the Arctic. The physical and biogeochemical features of every coastal area govern the main distribution patterns of freshly introduced PCBs into the marine system. Some of these processes are determined by chemical properties of the individual PCB congener. Thus, atmospheric influx along with ad/absorption on non-living organic material, photolytical and biological degradation processes vary from one PCB congener to another. For a detailed fate analysis of individual congeners, we developed a new chemical model, based on the GOTM-ECOSMO-FABM model framework. Here, we exemplarily present results for PCB153 based on 1D simulations of four regions in the North-Baltic Sea. The study area is characterized by different hydrodynamic and biogeochemical conditions. We investigate the impact of resuspension, mixing and the biological pump, sea ice and tides on the final phasal distribution of PCB153. Different combinations of these factors lead to the development of different areas of PCB153 accumulation, with the formation of hotspot areas, and influence the total uptake and concentration of PCB153 in the water column. As a result, two major dynamics determine the fate of PCB153 in the coastal ocean: (i) Primary production leads to PCB153 being adsorbed by organic material. Partitioning to organic material and sedimentation of organic particles removes dissolved PCB153 from the surface ocean and increases atmospheric influx. (ii) Tidal-induced resuspension and mixing control the benthic–pelagic exchange of PCB153 and its distribution in the water column. Depending on the resuspension regime and stratification, sediments can become a permanent (Gotland Deep, the Baltic Sea) or seasonal sink for PCB153. In regions with seasonal stratification and high near bottom turbulence (Northern North Sea), resuspension events can lead to pronounced peaks in PCB153 concentrations and can therefore have a major impact on bioaccumulation. Under the conditions of permanent mixing and high bottom turbulence (Southern North Sea, Bothnian Bay), pollutants are hardly accumulating in sediments.
    Type of Medium: Online Resource
    ISSN: 2073-4441
    URL: Article
    DOI: 10.3390/w14233952
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2521238-2
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  • 4
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    Online Resource
    Understanding the Role of Organic Matter Cycling for the Spatio-Temporal Structure of PCBs in the North Sea
    MDPI AG ; 2020
    In:  Water Vol. 12, No. 3 ( 2020-03-14), p. 817-
    Details
    In: Water, MDPI AG, Vol. 12, No. 3 ( 2020-03-14), p. 817-
    Abstract: Using the North Sea as a case scenario, a combined three-dimensional hydrodynamic-biogeochemical-pollutant model was applied for simulating the seasonal variability of the distribution of hydrophobic chemical pollutants in a marine water body. The model was designed in a nested framework including a hydrodynamic block (Hamburg Shelf Ocean Model (HAMSOM)), a biogeochemical block (Oxygen Depletion Model (OxyDep)), and a pollutant-partitioning block (PolPar). Pollutants can be (1) transported via advection and turbulent diffusion, (2) get absorbed and released by a dynamic pool of particulate and dissolved organic matter, and (3) get degraded. Our model results indicate that the seasonality of biogeochemical processes, including production, sinking, and decay, favors the development of hot spots with particular high pollutant concentrations in intermediate waters of biologically highly active regions and seasons, and it potentially increases the exposure of feeding fish to these pollutants. In winter, however, thermal convection homogenizes the water column and destroys the vertical stratification of the pollutant. A significant fraction of the previously exported pollutants is then returned to the water surface and becomes available for exchange with the atmosphere, potentially turning the ocean into a secondary source for pollutants. Moreover, we could show that desorption from aging organic material in the upper aphotic zone is expected to retard pollutants transfer and burial into sediments; thus, it is considerably limiting the effectiveness of the biological pump for pollutant exports.
    Type of Medium: Online Resource
    ISSN: 2073-4441
    URL: Article
    DOI: 10.3390/w12030817
    Language: English
    Publisher: MDPI AG
    Publication Date: 2020
    detail.hit.zdb_id: 2521238-2
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