ALBERT

Description: A newly developed coastal model, FESOM-C, based on three-dimensional unstructured meshes and finite volume, is applied to simulate the dynamics of the southeastern North Sea. Variable horizontal resolution enables coarse meshes in the open sea with refined meshes in shallow areas including the Wadden Sea and estuaries to resolve important small-scale processes such as wetting and drying, sub-mesoscale eddies, and the dynamics of steep coastal fronts. Model results for a simulation of the period from January 2010 to December 2014 agree reasonably well with data from numerous regional autonomous observation stations with high temporal and spatial resolutions, as well as with data from FerryBoxes and glider expeditions. Analyzing numerical solution convergence on meshes of different horizontal resolutions allows us to identify areas where high mesh resolution (wetting and drying zones and shallow areas) and low mesh resolution (open boundary, open sea, and deep regions) are optimal for numerical simulations.

Description: Structural properties and water dissolution of six sodium–aluminum–phosphate (NAP) glasses have been investigated before and after irradiation by a gamma-ray source based on 60Co. Two of these samples were of simple composition, and four samples had a complex composition with radionuclide simulants representing actinides, fission, and activated corrosion products. Samples of the simple composition are fully vitreous, whereas samples of the complex composition contained up to 10 vol.% of aluminum–phosphate, AlPO4, and traces of ruthenium dioxide, RuO2. Based on the study of pristine and irradiated glasses, it was established that the radiation dose of 62 million Gray had practically no effect on the phase composition and structure of samples. At the same time, the rate of leaching of elements from the irradiated samples by water was decreased by about two times.

Description: The key task in the solidification of high-level waste (HLW) into a magnesium potassium phosphate (MPP) compound is the immobilization of mobile cesium isotopes, the activity of which provides the main contribution to the total HLW activity. In addition, the obtained compound containing heat-generating radionuclides can be significantly heated, which increases the necessity of its thermal stability. The current work is aimed at assessing the impact of various methodological approaches to HLW solidification on the thermal stability of the MPP compound, which is evaluated by the mechanical strength of the compound and its resistance to cesium leaching. High-salt surrogate HLW solution (S-HLW) used in the investigation was prepared for solidification by adding sorbents of various types binding at least 93% of 137Cs: ferrocyanide K-Ni (FKN), natural zeolite (NZ), synthetic zeolite Na-mordenite (MOR), and silicotungstic acid (STA). Prepared S-HLW was solidified into the MPP compound. Wollastonite (W) and NZ as fillers were added to the compound composition in the case of using FKN and STA, respectively. It was found that heat treatment up to 450 °C of the compound containing FKN and W (MPP-FKN-W) almost did not affect its compressive strength (about 12–19 МPa), and it led to a decrease of high compressive strength (40–50 MPa) of the compounds containing NZ, MOR, and STA (MPP-NZ, MPP-MOR, and MPP-STA-NZ, respectively) by an average of 2–3 times. It was shown that the differential leaching rate of 137Cs on the 28th day from MPP-FKN-W after heating to 250 °C was 5.3 × 10−6 g/(cm2∙day), however, at a higher temperature, it increased by 20 and more times. The differential leaching rate of 137Cs from MPP-NZ, MPP-MOR, and MPP-STA-NZ had values of (2.9–11) × 10−5 g/(cm2∙day), while the dependence on the heat treatment temperature of the compound was negligible.

Description: Ocean mass variability on timescales of months to decades is still insufficiently understood. On these timescales, large-scale ocean bottom pressure (OBP) anomalies are associated both with wind induced variability as well as baroclinic processes, i.e. related to vertical shear of ocean density. The GRACE mission has been instrumental in quantifying such mass fluctuations, yet its lifetime is limited. The broader importance of non-tidal ocean mass variability for oceanography but also geodesy (i.e. for understanding the time-varying geoid, shape of the Earth's crust, centre of figure, Earth rotation) is obvious. Deep ocean processes can only be understood properly when not only sea surface height and upper ocean steric expansion are measured but deep ocean pressure anomalies are accounted for in addition. Apart from GRACE, the SWARM constellation may provide information on the lowest degrees of the time-variable gravity field of the Earth and therefore of large-scale oceanic processes. Here we introduce the project CONTIM, which is run in the framework of the German Special Priority Programme "Dynamic Earth" (SPP1788). In CONTIM we propose to combine expertise on precise satellite orbit determination, gravity field and mass modelling, and physical oceanography to retrieve, analyse and verify consistent time series of ocean mass variations from a set of low-flying Earth orbiters including GRACE, but extending the GRACE time series. This information is used to advance our understanding of oceanic movement, ocean warming and sea level rise. CONTIM will thus synergistically address three areas: (1) the methodology of precisely determining LEO orbits, applied here to the SWARM constellation. (2) a new method of retrieving large-scale time-varying gravity (TVG) and mass change associated with oceanic (and cryospheric and hydrological) processes from results of (1), based on forward modelling. (3) physical modelling of ocean mass variations, both for improved forward modelling in (2) and for integration with satellite-geodetic retrieved ocean mass, and aiding in the determination of a final consistent modelling of sea level rise, ocean warming and oceanic mass budget. In this contribution, we will give an overview of the objectives of the project and provide some first results. We will highlight the technical challenges associated with the computation of kinematic SWARM orbits. Furthermore, different scenarios for time-variable gravity field retrieval are tested and evaluated, and the CHAMP data are used to test the methods over a longer period. To better understand and parameterize the ocean mass signals, we will discuss output from a high resolution version of the ocean model FESOM forced with tides, surface winds and atmospheric pressure.

Description: We propose to make the damping time scale, which governs the decay of pseudo-elastic waves in the Elastic Viscous Plastic (EVP) sea-ice solvers, independent of the external time step and large enough to warrant numerical stability for a moderate number of internal time steps. A necessary condition is that the forcing on sea ice varies slowly on the damping time scale, in which case an EVP solution may still approach a Viscous Plastic one, but on a time scale longer than a single external time step. In this case, the EVP method becomes very close to the recently proposed modified EVP (mEVP) method in terms of stability and simulated behavior. In a simple test case dealing with sea ice breaking under the forcing of a moving cyclone, the EVP method with an enlarged damping time scale can simulate linear kinematic features which are very similar to those from the traditional EVP implementation, although a much smaller number of internal time steps is used. There is more difference in sea-ice thickness and linear kinematic features simulated in a realistic Arctic configuration between using the traditional and our suggested choices of EVP damping time scales, but it is minor considering model uncertainties associated with choices of many other parameters in sea-ice models.