Numerical simulation of M2 internal tides in the south Brazil Bight and their interaction with the Brazil currente

Abstract

A fully three-dimensional nonlinear primitive equation ocean model is applied tostudy the semidiurnal internal tide in the South Brazil Bight under summer conditions.Along the shelf break and upper slope of this region, the upper layer (0–600 m) isoccupied by the southward flowing Brazil Current. Several numerical experiments wereconducted to investigate the generation and propagation of the M2internal tide. Usinghorizontally homogeneous and vertically stratified density fields, internal tides weregenerated over the whole Bight with a clear signal on the continental shelf. When a morerealistic summer stratification was considered, a baroclinic jet, representative of the BrazilCurrent, developed and comparisons between current observations and modeled resultswere improved. This jet acts as a barrier to the coastward propagation of the internal tidegenerated over the slope, reflecting it back towards the open ocean. On the negativerelative vorticity side of the Brazil Current, located over the shelf, internal tides aretrapped, enhancing vertical current variability and, hence, tidally induced mixing. Theresults highlight the importance of considering background flows when investigating internal tides in regions of strong along-slope baroclinic flows such as western boundary currents.