On the Black Sea circulation with very strong and weak winds

Abstract

With a baroclinic prognostic model of sea dynamics, the annual cycle of the Black Sea hydrological regime is modeled for constantly changing atmospheric circulation types characteristic of the Black Sea. Emphasis is placed on the hydrological structure of the upper sea layer in two extreme meteorological situations, storm and near-calm conditions over the sea basin. A significant difference is found in the character of the sea currents, and the main sea circulation features are determined for such situations. The system of model equations is solved using a method of two-cycle splitting on a grid with a 5-km horizontal step and 32 levels in the vertical.Wind is one of the main factors forming systems of currents in the seas and oceans. Therefore, the hydrological structure in water basins is largely determined by meteorological regimes over them. The multiyear meteorological observations over the Black Sea show that atmospheric processes over the sea have large variability and diversity of circulation regimes [1,16]. Wind stress is the main external factor exciting drift currents. It forms a specific Black Sea circulation regime under conditions of Earth's rotation together with internal factors, such as baroclinity, coasline, and bottom relief.One of the most important goals of the Black Sea oceanography is to study the Black Sea circulation processes in close connection with the atmospheric circulation and to obtain quantitative circulation characteristics of the sea. It cannot be solved using experimental methods only.The goal of this paper is a numerical study of the Black Sea hydrological structure in storm and nearcalm conditions representing two extreme atmospheric states in a wide range of circulation regimes developing over the Black Sea. Such meteorological situations are not rare over the Black Sea. Therefore, the study of the main features of the sea currents in these extreme situations is of special interest. Besides, some features of the circulation of the Black Sea waters in storm and calm conditions can be observed in intermediate meteorological situations.The annual cycle of the Black Sea hydrological regime was modeled using a baroclinic model of the sea dynamics [6, 7, 18] with continuously changing atmospheric circulation processes typical of the Black Sea basin. The proposed model is an improved version of the model of Black Sea dynamics developed earlier [5,8,[12][13][14]. It is based on the full system of the ocean hydrothermodynamic equations in a hydrostatic approximation. The system of equations is written in the Cartesian rectangular coordinate system for deviations of thermodynamic values (temperature, pressure, and density) from the standard vertical distributions. The empirical Mamaev formula [10] is used as the equation of state of seawater. Unlike [5,8,[12][13][14], the model considers water exchange between the Black Sea and the Sea of Marmara through the Bosporus, the Danube runoff, absorption of total solar radiation in the upper sea layer, spatial and temporal variation of the c...