Numerical Experiments on Modeling of the Black Sea Deep Currents

Abstract

Modeling results of the Black Sea deep-water current reconstruction are considered. Computations are provided by applying the nonlinear z-coordinate model developed in Marine Hydrophysical Institute (MHI). Climatic atmospheric forcing and the atmospheric reanalysis data (ALADIN, Era-Interim) obtained for 2006, 2010 and 2013 are taken into account in different numerical experiments. The Black Sea climatology experiment is performed with a spatial grid step equal to 5 km, and in other experiments the 1.6 km grid step is used. Three-dimensional structure of the Black Sea currents on 45 levels within the surface horizon (2.5 m) and the bottom one (2100 m) is reconstructed. The anticyclonic current (countercurrent) extending along the Black Sea continental slope in direction opposite to the Rim Current is detected at about 1000 m and deeper. In the climatic fields the countercurrent exists in spring and summer in the northern part of the basin. In the experiments that included the reanalysis forcing, the countercurrent is revealed as separate streams in various continental slope areas and in different seasons. Its mean velocity is about 5 cm/s, the highest one is equal to 10 cm/s. In the overlying layer in the northeastern part of the Black Sea, the countercurrent is also detected by modeling as well as it is revealed by CTD and ADCP measurements.

Undercurrents in the Northeastern Black Sea Detected on the Basis of Multi-Model Experiments and Observations

“…For further analysis, all the data were grouped according to the sea characteristic layers: the subsurface layer (0-5 m), the upper mixed layer (5-30 m), the cold intermediate layer (CIL, 30-100 m), and the main pycnocline layer (100-300 m). The subpycnocline layer was divided into two parts: the first one from 300 to 800 m and the second one from 800 to 1500 m. The horizon of 800 m was chosen due to the effect of increasing current velocity found in our previous works at depths of 800-1000 m [18,48], which were performed in the framework of MERSEA Class 4 metrics [49]. Finally, 1500 m is the maximum profiling depth of the Black Sea ARGO floats in 2011.…”

“…There are also arguments in favor of the absence of a basin-scale undercurrent flow [16,17]. When studying the dynamics of the Black Sea on the basis of the MHI model [18], anticyclonic jet currents were found in the velocity field, propagating along the continental slope in some areas. In the northeastern part of the sea, the modeled undercurrent was found quasi-periodically, in springs and summers of several years.…”

Reconstruction of the Black Sea Deep-Water Circulation Using INMOM and Comparison of the Results with the ARGO Buoys Data

“…G. Neumann in his work * 1942 adhered to the hypothesis on this issue, suggesting the presence of a two-layer system of currents in the Black Sea (BS). According to his hypothesis, a cyclonic direction prevails in the upper layer of this system, but the sign of the currents changes with depth, and a deep-water countercurrent occurs on the 300 m horizon with subsequent intensification to the 1000 m horizon [1].…”

“…According to [3], which came out almost half a century after G. Neumann hypothesis, there are no reliable climatic data for the deep-water layers below the 300 m horizon, allowing to draw any definite conclusions about the deep-water circulation direction. Currently, according to [1], research continues on the directivity of the BS deep-water circulation, including theoretical calculations and laboratory experiments, to substantiate the presence or absence of deep-water countercurrent [4]. The ambiguity of the solution of this problem is due to the fact that both cyclonic and anticyclonic type of the BS deep circulation do not contradict the general physical understanding of its circulation.…”

“…In recent years, the possibilities of numerical modeling of the three-dimensional water dynamics have reached a completely different level, which, perhaps, was the reason for the increased interest in the direction of the BS circulation of the deep-water circulation. Currently, the most active research work in this field is being conducted by a group of scientists from Marine Hydrophysical Institute (MHI) of the Russian Academy of Sciences (see, for example, [1] and research *).…”