Seasonal and Vertical Variability of Currents Energy in the Sub-Mesoscale Range on the Black Sea Shelf and in its Central Part

Abstract

Purpose. The study is aimed at investigating seasonal variability and vertical distribution of the submesoscale currents energy (scales L = 1 ... 10 km, T = 1 ... 10 days) in the deep and shelf zones of the Black Sea. Methods and Results. The study is based on the spectral analysis of the results obtained from the NEMO model numerical calculations performed with high spatial resolution 1 km. The analysis shows that in the areas under investigation, seasonal variability of the sub-mesoscale currents energy is significantly different. At that, in both regions, seasonal variation of energy of the sub-mesoscale currents whose scale is less than 10 km (Esp) is in good agreement with that of the density fluctuations on the same scales. In the central part of the sea, the high values of (Esp) are concentrated in the upper mixed layer throughout the whole year. The (Esp) peak is observed in winter at the depths 0–40 m, which indicates the important role of baroclinic instability (induced by the inhomogeneous distribution of the upper mixed layer during this period) in generation of sub-mesoscale processes in the Black Sea. At the same time, in February in the central part of the northwestern shelf, an absolute minimum of (Esp) is observed due to complete mixing and barotropization of the water column. The (Esp) maximum values are noted in September – October, that is related to intensification of the desalinated water cross-shelf transport from the river mouths being affected by the synoptic eddies. At the same time, in the autumn period in this region, the (Esp) high values are observed in the layer, the thickness of which is higher than that in summer (as well as in the central part of the sea). Dynamics of the (Esp) values distribution corresponds to the time variation of the upper mixed layer thickness. Variability of the sub-mesoscale currents energy is of a pulsating character with the short-term intensifications and weakenings. Such variability is significantly related to passing of the synoptic fronts and the cross-shelf water transport being influenced by the eddies and upwellings, which lead to baroclinic instability of waters. Conclusions. Seasonal and vertical variability of the spectral energy in the Black Sea deep and shelf zones testifies in favor of the decisive role of the water baroclinic instability arising due to heterogeneity of the upper mixed layer.

Cross‐Slope Buoyancy Fluxes Cause Intense Asymmetric Generation of Submesoscale Eddies on the Periphery of the Black Sea Mesoscale Anticyclones

“…Our analysis indicates that the rise of BCI, in this case, is related to the growth of the mixed layer in the Black Sea in agreement with recent study of Puzina et al. (2021). The instability of the upper mixed layer caused by the impact of heterogeneous wind and convective mixing is the probable reason for the intense generation of SE in winter (see Callies et al., 2015).…”

“…Submesoscale dynamics is characterized by significant seasonal and interannual variability (Buckingham et al., 2016; Callies et al., 2015; Capet et al., 2008; Puzina et al., 2021). Several authors showed that in many regions of the World, including the Black Sea (Puzina et al., 2021) it intensifies in winter due to the baroclinic instability of the deep winter mixed layer (Callies et al., 2015; Capet et al., 2008; Mensa et al., 2013; Puzina et al., 2021).…”

“…Submesoscale dynamics is characterized by significant seasonal and interannual variability (Buckingham et al., 2016; Callies et al., 2015; Capet et al., 2008; Puzina et al., 2021). Several authors showed that in many regions of the World, including the Black Sea (Puzina et al., 2021) it intensifies in winter due to the baroclinic instability of the deep winter mixed layer (Callies et al., 2015; Capet et al., 2008; Mensa et al., 2013; Puzina et al., 2021). During the warm period of the year, the important reasons for the generation of SE: are frontogenesis (Thomas & Ferrari, 2008), topographic and shear instability of currents (Aleskerova et al., 2021; Gula et al., 2015; McWilliams, 2016; Zatsepin et al., 2011).…”

Submesoscale Currents from UAV: An Experiment over Small-Scale Eddies in the Coastal Black Sea

“…A suitable testbed for SME investigation is the Black Sea thanks to its well-developed observational and theoretical scientific facilities [4,5]. Various SME studies are performed for the Black Sea using satellite data [6][7][8] and numerical simulations [9][10][11]. They show, particularly, that SMEs can significantly impact coastal material transport [5,12] and vertical and horizontal distribution of bio-optical characteristics in the basin [13].…”