Citation: Korotenko, K.; Osadchiev, A.; Melnikov, V. Mesoscale Eddies in the Black Sea and Their Impact on River Plumes: Numerical Modeling and Satellite Observations. Remote Sens. 2022, 14, 4149. https://doi.org/ 10.3390/rs14174149 Academic Editor: Yukiharu Hisaki Received: 2 July 2022 Accepted: 16 August 2022 Published: 24 August 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). remote sensing Article Mesoscale Eddies in the Black Sea and Their Impact on River Plumes: Numerical Modeling and Satellite Observations Konstantin Korotenko 1, *, Alexander Osadchiev 1,2 and Vasiliy Melnikov 1 1 Shirshov Institute of Oceanology, Russian Academy of Sciences, Nakhimovskiy Prospect 36, 117997 Moscow, Russia 2 Moscow Institute of Physics and Technology, Institusky Lane 9, 141701 Dolgoprudny, Russia * Correspondence: korotenko.ka@ocean.ru Abstract: The Northeast Caucasian Current (NCC) is the northeastern part of the cyclonic Rim Current (RC) in the Black Sea. As it sometimes approaches the narrow shelf very closely, topographically generated cyclonic eddies (TGEs) can be triggered. These eddies contribute to intense, along- and cross-shelf transport of trapped water with enhanced self-cleaning effects of the coastal zone. Despite intense studies of eddy dynamics in the Black Sea, the mechanisms of the generation of such coastal eddies, their unpredictability, and their capacity to capture and transport impurities are still poorly understood. We applied a 3-D low-dissipation model DieCAST/Die2BS coupled with a Lagrangian particle transport model supported by analysis of optical satellite images to study generation and evolution of TGEs and their effect on river plumes unevenly distributed along the northeastern Caucasian coast. Using the Furrier and wavelet analyses of kinetic energy time series, it was revealed that the occurrence of mesoscale TGEs ranges from 10 up to 50 days. We focused on one particular isolated anticyclonic TGE that emerged in late fall as a result of instability of the RC impinging on the abrupt submarine area adjoining the Pitsunda and Iskuria capes. Being shed, the eddy with a 30-km radius traveled along the coast as a coherent structure during ~1.5 months at a velocity of ~3 km/day and vertical vorticity normalized by the Coriolis parameter ~(0.1 ÷ 1.2). This eddy captured water from river plumes localized along the coast and then ejected it to the open sea, providing an intense cross-shelf transport of riverine matter. Keywords: topographically generated mesoscale eddies; relative vorticity; river plumes; eddy-plume interaction; DieCAST model; Lagrangian modeling; wavelet analysis; Black Sea 1. Introduction Coastal mesoscale eddies widely emerging in the ocean play an important role in physical, biological, and geochemical processes. They may considerably affect transport, accumulation, and dispersion of pollutants [1–3], floating organisms [4–8], phytoplank- ton [9], and microplastic pollution in the sea, which have received large attention during the last decade [10–12]. In this study, we focus on mesoscale eddies in the semi-enclosed Black Sea. Being one of the main features of the general Black Sea circulation, the basin-scale cyclonic boundary current, referred to as the Rim Current (RC), is forced by the local wind curl together with thermohaline circulation driven by non-uniform surface fluxes [13–20]. Analysis of extensive CTD and ADCP measurements together with satellite observations revealed that the RC is a well-pronounced meandering jet stream confined over the steepest topographic slope which separates shelf areas and often associated cyclonic–anticyclonic eddy pairs located on both of its sides [17,21–23]. The strong-boundary RC limits the water and matter exchange between the shelf and open sea. On the other hand, meandering of the RC and the resulting formation of instabili- ties manifested by mesoscale eddies, filaments, dipole structures, etc., could significantly Remote Sens. 2022, 14, 4149. https://doi.org/10.3390/rs14174149 https://www.mdpi.com/journal/remotesensing