Barotropic instability process of Brazil current at Santos Basin / Processos de instabilidade barotrópica da Corrente do Brasil na Bacia de Santos

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

The Brazil Current (BC) is formed at the bifurcation of the southern branch of the South Equatorial Current and flows south-southeastward off the east, southeast and southern Brazilian continental margin, exhibiting intense meso-scale activity between the Vitória-Trindade Ridge (20oS) and Cape Santa Marta Grande (28oS). The knowledge of such activity, built over time, refers mainly to the frontal meanders and eddies. The edge vortical structures as a dipole configuration are reported only through AVHRR images. Thus, we aimed to characterize the dynamical structure of a BC vortical dipole, observed in the Santos Basin, with a quasi-synoptic velocity (vessel-mounted ADCP) and hydrographic (CTD) dataset from DEPROAS V cruise. The objective mapping of structures captured by the cruise sampling grid was the departing point for the description of the dipole and evaluation of its degree of geostrophy. The fields of the stream function showed a classic pattern of a dipole with cyclonic and anticyclonic eddies positioned on opposite sides of the current axis. On average, the diameter of the two eddies was around 110 km in their largest axes. Then, as the Rossby number was 0.27, we advanced in investigating the issues involving the dynamic structure by we approximating the ocean to a 11/2 layer quasi-geostrofic model derived from the observations and dynamically calibrated. Burger number revealed that both relative and stretching vorticity were competing for the dynamics of the system. The comparison between the modeled stream function and potential vorticity fields showed that both the dipole and the BC flow were not in a stationary state. Finally, evidences of reinforcement between the eddies of the dipole were obtained through the interaction between the field of the stream function of vortical structure with the field of potential vorticity of the other one, and vice-versa. Therefore, we conclude that the dipole were in a barotropic growth process.

ASSUNTO(S)

dipolos vorticiais dipoles eddies corrente do brasil vórtices brazil currents barotropic instability bacia de santos

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