Numerical study on the planetary Rossby modes in the Black Sea

We address in this paper the planetary basin modes and their possible impac t on the circulation of Black Sea. These oscillations could become importan t in semi-enclosed seas where the horizontal scales are smaller than the ba rotropic radius of deformation and the baroclinic radius of deformation is comparable with the basin scales. The physical balances studied here are ba sed on theoretical results for the Rossby modes in rectangular basins and o n model simulations carried out with Bryan-Cox ocean model with eddy resolu tion. Eddies with horizontal scales of 100-200 km spontaneously form and pr opagate to the west with phase velocity of few kilometers per day. External mode oscillations dominate the model solution and show close similarity wi th estimates based on simplistic theoretical models. In the baroclinic ocea ns these oscillations trigger active baroclinic variability and western pro pagation, but with strongly modified wave characteristics in comparison to the barotropic case. The comparisons between simulations and data from surv eys and altimeters demonstrates that the planetary modes are a dominating f orm of wave motion in this sea and can explain the westward propagation of signals in its deep part. It is suggested that the excitation of rotational modes can be also important for the dispersion of tracers. (C) 1999 Elsevi er Science B.V. All rights reserved.