Seasonal and interannual variability of Black Sea hydrophysical fields reconstructed from 1971–1993 reanalysis data

We pioneered a retrospective analysis of Black Sea hydrophysical fields for the period from 1971 to 1993. We describe a reanalysis algorithm based on the assimilation (in a σ-coordinate circulation model) of observed temperature and salinity data obtained on hydrophysical test areas. The thickness of the cold intermediate layer (CIL) and its freezing capacity for 1985 to 1993 were found to be increasing. At the levels of 0, 50, 75, and 100 m, the tendency of variations in annual values of level-averaged temperature is negative. At the level of 200 m and deeper, the linear trends of the interannual course of temperature are positive. We found that the linear trends of interannual variations in salinity are negative in the upper layer of 0 to 50 m and positive at 75 m and deeper. The sea-water circulation in the layer from 0 to 300 m was observed to be maximum in February–March and minimum in September–October. The characteristic of the linear trend of interannual variations in the kinetic energy of currents averaged over the sea surface is negative, while its value is positive in the layer from 50 to 100 m. Some factors responsible for the formation of hydrophysical fields in the sea and their seasonal and interannual variations were indicated. We revealed that there is a qualitative resemblance between seasonal and interannual variations [4, 26] in temperature, salinity, and kinetic energy.