Lagrangian pathways under the Filchner-Ronne ice shelf and in the Weddell Sea

Peer reviewe

Mathematical modelling of the dynamics and containment of COVID‑19 in Ukraine

COVID-19 disease caused by the novel SARS-CoV-2 coronavirus has already brought unprecedented challenges for public health and resulted in huge numbers of cases and deaths worldwide. In the absence of effective vaccine, different countries have employed various other types of non-pharmaceutical interventions to contain the spread of this disease, including quarantines and lockdowns, tracking, tracing and isolation of infected individuals, and social distancing measures. Effectiveness of these and other measures of disease containment and prevention to a large degree depends on good understanding of disease dynamics, and robust mathematical models play an important role in forecasting its future dynamics. In this paper we focus on Ukraine, one of Europe’s largest countries, and develop a mathematical model of COVID-19 dynamics, using latest data on parameters characterising clinical features of disease. For improved accuracy, our model includes age-stratified disease parameters, as well as age- and location-specific contact matrices to represent contacts. We show that the model is able to provide an accurate short-term forecast for the numbers and age distribution of cases and deaths. We also simulated different lockdown scenarios, and the results suggest that reducing work contacts is more efficient at reducing the disease burden than reducing school contacts, or implementing shielding for people over 60

A fully coupled 3D wave-current interaction model on unstructured grids

We present a new modeling system for wave-current interaction based on unstructured grids and thus suitable for very large-scale high-resolution multiscale studies. The coupling between the 3D current model (SELFE) and the 3rd generation spectral wave model (WWM-II) is done at the source code level and the two models share same sub-domains in the parallel MPI implementation in order to ensure parallel efficiency and avoid interpolation. We demonstrate the accuracy, efficiency, stability and robustness of the coupled SELFE-WWM-II model with a suite of progressively challenging benchmarks with analytical solution, laboratory data, and field data. The coupled model is shown to be able to capture important physics of the wave-current interaction under very different scales and environmental conditions with excellent convergence properties even in complicated test cases. The challenges in simulating the 3D wave-induced effects are highlighted as well, where more research is warranted

Transport and Fate of 137Cs Released From Multiple Sources in the North Atlantic and Arctic Oceans

The North Atlantic and Arctic oceans, along with the North Pacific, are the main reservoirs of anthropogenic radionuclides introduced in the past 75 years. The POSEIDON-R compartment model was applied to the North Atlantic and Arctic oceans to reconstruct 137Cs contamination in 1945–2020 due to multiple sources: global fallout, exchange flows with other oceans, point-source inputs in the ocean from reprocessing plants and other nuclear facilities, the impact of the Chernobyl accident and secondary contamination resulting from river runoff and redissolution from bottom sediments. The model simulated the marine environment as a system of 3D compartments comprising the water column, bottom sediment, and biota. The dynamic model described the transfer of 137Cs through the pelagic and benthic food chains. The simulation results were validated using the marine database MARIS. The calculated concentrations of 137Cs in the seaweed and non-piscivorous and piscivorous pelagic fish mostly followed the concentration of 137Cs in water. The concentration in coastal predator fish lagged behind the concentration in water as a result of a diet that includes both pelagic and benthic organisms. The impact of each considered source on the total concentration of 137Cs in non-piscivorous fish in the regions of interest was analyzed. Whereas the contribution from global fallout dominated in 1960–1970, in 1970–1990, the contribution of 137Cs released from reprocessing plants exceeded the contributions from other sources in almost all considered regions. Secondary contamination due to river runoff was less than 4% of ocean influx. The maximum total inventory of 137Cs in the Arctic Ocean (31,122 TBq) was reached in 1988, whereas the corresponding inventory in the bottom sediment was approximately 6% of the total. The general agreement between simulated and observed 137Cs concentrations in water and bottom sediment was confirmed by the estimates of geometric mean and geometric standard deviation, which varied from 0.89 to 1.29 and from 1.22 to 1.87, respectively. The approach used is useful to synthesize measurement and simulation data in areas with observational gaps. For this purpose, 13 representative regions in the North Atlantic and Arctic oceans were selected for monitoring by using the “etalon” method for classification

Modeling of transformation of surface wave packets interacting with abrupt bottom change

The paper presents results of numerical modelling on interaction of linear surface wavetrains with a bottom step. Small-amplitude wavetrains with different wavelengths are examined. Dependence of the transformation coefficients (transmission and reflection coefficients) of surface waves on the ratio of the depths before and after the step is obtained. Applicability of the hydrostatic approximation to simulation of wave transformation is discussed. It is shown that the hydrostatic model can be used for the modelling of wavetrains with sufficiently long career waves. Transformation coefficients obtained in this case are in a good agreement with analytical formulae. The results obtained on the basis of earlier developed numerical code are in agreement with results obtained by means of freely available package MITgcm

Sediment and Radioactivity Transport in the Bohai, Yellow, and East China Seas: A Modeling Study

This paper is concerned with the development of a radionuclide dispersion model for the nuclear power plants in the Bohai, Yellow, and East China seas (BYECS) characterized by high turbidity and multi-scale circulations, focusing on the comparison of dispersion processes of 137Cs depending upon, in particular, the suspended sediment concentration and erosion/sedimentation processes. The simulations were carried out using a multi-fraction sediment transport model embedded in the semi-implicit Eulerian–Lagrangian finite-element coupled wave-circulation model linked with the model of radionuclide transport, which describes the key radionuclide transfer processes in the system of water–multi-fraction sediments. In contrast to the Eulerian models used for hydrodynamics and sediment transport processes, the Lagrangian technique was applied to simulate the transport of radionuclides. The simulation results for total suspended concentration agreed with in situ measurements and the Geostationary Ocean Color Imager data. The results of the simulation of hypothetical releases of 137Cs from four nuclear power plants (NPPs) placed in BYECS essentially differ from the real release of activity in the Pacific Ocean shelf due to the Fukushima Daiichi accident, which took place at the same time and released activity that was similar. The total amount of bottom contamination of 137Cs in releases from the Sanmen, Hanbit, and Hongyanhe NPPs was about 40% of dissolved component, and the total amount of suspended component was about 20% of dissolved component, in contrast with the Fukushima Daiichi accident, where the particulate component was only 2%. The results demonstrate the importance of erosion processes in the budget of 137Cs in shallow areas around the Sanmen and Hanbit NPPs, where strong wind and tidal currents took place

Sediment and Radioactivity Transport in the Bohai, Yellow, and East China Seas: A Modeling Study

This paper is concerned with the development of a radionuclide dispersion model for the nuclear power plants in the Bohai, Yellow, and East China seas (BYECS) characterized by high turbidity and multi-scale circulations, focusing on the comparison of dispersion processes of 137Cs depending upon, in particular, the suspended sediment concentration and erosion/sedimentation processes. The simulations were carried out using a multi-fraction sediment transport model embedded in the semi-implicit Eulerian–Lagrangian finite-element coupled wave-circulation model linked with the model of radionuclide transport, which describes the key radionuclide transfer processes in the system of water–multi-fraction sediments. In contrast to the Eulerian models used for hydrodynamics and sediment transport processes, the Lagrangian technique was applied to simulate the transport of radionuclides. The simulation results for total suspended concentration agreed with in situ measurements and the Geostationary Ocean Color Imager data. The results of the simulation of hypothetical releases of 137Cs from four nuclear power plants (NPPs) placed in BYECS essentially differ from the real release of activity in the Pacific Ocean shelf due to the Fukushima Daiichi accident, which took place at the same time and released activity that was similar. The total amount of bottom contamination of 137Cs in releases from the Sanmen, Hanbit, and Hongyanhe NPPs was about 40% of dissolved component, and the total amount of suspended component was about 20% of dissolved component, in contrast with the Fukushima Daiichi accident, where the particulate component was only 2%. The results demonstrate the importance of erosion processes in the budget of 137Cs in shallow areas around the Sanmen and Hanbit NPPs, where strong wind and tidal currents took place