Seasonal, interannual, and mesoscale variability of the Black Sea upper layer circulation derived from altimeter data

TOPEX/Poseidon and ERS altimeter data comprising the period from May 1992 to May 1999 are assimilated into a shallow water model for providing a dynamically consistent interpretation of the sea surface height variations and estimation of the temporal and spatial characteristics of the upper layer circulation in the Black Sea. These 7-year-long observations offer a new capability for interpretation of major transient and quasi-permanent features of the upper layer circulation. The instantaneous flow fields involve a complex, eddy-dominated system with different types of structural organizations in which the eddies and the gyres of the interior cyclonic cell interact continuously among themselves and with meanders, and filaments of the Rim Current. The circulation possesses a distinct seasonal cycle whose major characteristic features repeat every year with some year-to-year variability. An organized two-gyre winter circulation system disintegrates gradually into a series of interconnecting eddies in the summer and autumn months, which are also characterized by more pronounced and complex mesoscale activity in the peripheral flow system. Our analyses suggest a revised schematic circulation picture of the major quasi-permanent and recurrent elements of the Black Sea.