Effects of lateral processes on the seasonal water stratification of the Gulf of Finland: 3-D NEMO-based model study

This paper aims to fill the gaps in knowledge of processes affecting the seasonal water stratification in the Gulf of Finland (GOF). We used a state-of-the-art modelling framework NEMO (Nucleus for European Modelling of the Ocean) designed for oceanographic research, operational oceanography, seasonal forecasting, and climate studies to build an eddy-resolving model of the GOF. To evaluate the model skill and performance, two different solutions were obtained on 0.5 km eddy-resolving and commonly used 2 km grids for a 1-year simulation. We also explore the efficacy of non-hydrostatic effect (convection) parameterizations available in NEMO for coastal application. It is found that the solutions resolving submesoscales have a more complex mixed layer structure in the regions of the GOF directly affected by the upwelling/downwelling and intrusions from the open Baltic Sea. Presented model estimations of the upper mixed layer depth are in good agreement with in situ CTD (BED) data. A number of model sensitivity tests to the vertical mixing parameterization confirm the model's robustness. Further progress in the submesoscale process simulation and understanding is apparently not connected mainly with the finer resolution of the grids, but with the use of non-hydrostatic models because of the failure of the hydrostatic approach at submesoscale

Filamentation of the surface plasma layer during the electrical explosion of conductors in strong magnetic fields

International audienceA model has been considered to describe the development of a surface discharge over a conductor electrically exploding in a strong magnetic field. A simulation performed using this model has shown that in the initial stage of the conductor explosion, a plasma layer of several tens of micrometers thick with an electron temperature of several electronvolts is formed on the metal surface. Based on the theory of small perturbations, the development of thermal filamentation instabilities that form in the surface plasma layer has been analyzed. The characteristic growth rates and wavelengths of these instabilities have been determined. The theoretical results were compared with the results of experiments performed on the ZEBRA generator (providing load currents of amplitude about 1 MA and rise time about 100 ns) and on the MIG generator (providing load currents of amplitude about 2 MA and rise time about 100 ns). For the conditions implemented with these generators, the filamentation model gives rise times of thermal filamentation instabilities of tens of nanoseconds at characteristic wavelengths of the order of 100 μm. These values are in good agreement with experimental data, which indicates the adequacy of both the surface discharge development model and the filamentation model