Numerical estimation of the Black Sea circulation near the continental slope using SKIRON and ERA5 atmospheric forcing

It is well known that the circulation in the upper sea layer is significantly depended on atmospheric fluxes. However, the influence of atmospheric forcing on the structure of deep-water circulation is not so obvious. For the Black Sea, this problem is complicated by the presence of a strong vertical density gradient (permanent pycnocline) which blocks seawater vertical exchange. This work presents model estimations of the Black Sea thermohaline and dynamic fields at different depths, obtained as a result of numerical simulations using various atmospheric forcing. The model circulation is driven by the input fields of wind stress, heat fluxes, precipitation and evaporation according to SKIRON and ERA5 data with a resolution of 0.1° and 0.25°, respectively. Numerical simulations are carried out based on the eddy-resolving z-model of the Marine Hydrophysical Institute RAS without data assimilation. 2016 is selected as test period due to the large amount of observational data. Open access data of ARGO floats positioning and profiling, as well as R/V Cruise measurement data are used to validate the simulation results.

It was found that the Black Sea thermohaline structure is reconstructed more accurately when using ERA5 forcing compared to the experiment using SKIRON. The temperature RMSE between the model and measurement data decreases on average by 27%, the salinity RMSE – by 20% in the layer from 0 to 1500 m. In the velocity field, an intensification of the cyclonic current is observed at the periphery of the basin in the upper 50-m layer. The change in the direction of the alongshore subpycnocline current from the northwestern (cyclonic) to the northeastern (anticyclonic) is modeled near the northeastern continental slope, and is confirmed by the trajectory of the ARGO float ID6901833 drifting at a parking depth of 200 m.