Sea level variations and their dependency on meteorological and hydrological forcing: Analysis of altimeter and surface data for the Black Sea

Abstract

TOPEX/Poseidon (T/P) altimeter data in the Black Sea are analyzed for almost 5 years in parallel with available hydrological and meteorological data with the aim of studying the water balance and the dependency of sea level oscillations on meteorological and hydrological forcing. This forcing induces seasonal variations of mean sea level with oscillations of ∼10–15 cm. The consistency between satellite and tidal gauge data is demonstrated in several coastal locations, and a mean ascending trend of ∼3 cm yr−1 is found in the two data sets. The variability in all components of water balance, including the Bosphorus outflow calculated as the difference between the fresh water flux and the time rate of sea level change estimated from altimeter data, is analyzed. The T/P data give very clear signals in the patterns of amplitudes of oscillations at intraannual, seasonal, and interannual timescales that help in understanding the variability of circulation. The intraannual variations are well pronounced on the continental slope and shelf and reach highest amplitudes in the areas of Sevastopol and Batumi quasi‐permanent eddies. The clearest representation of oscillations with seasonal periodicity exists in the area of Batumi Eddy. This variability is associated with the transition between states with intense cyclonic circulation in winter and weaker (sometimes anticyclonic) circulation in summer‐fall period. The Sevastopol Eddy is not clearly resolved in the seasonal variability. The interannual variability has the strongest signature in the area of western gyre and southeastern Black Sea. The analysis of satellite data supports some earlier studies on the circulation based on dynamic computations and numerical modeling. They make it possible to estimate the amount of water exchanged between coastal and open ocean areas caused by the time variability in the Ekman drift. The good quality of altimeter data and the high level of signals could ensure more accurate numerical simulations by means of data assimilation.