Circulação de baixa frequência no canal da Ilha Grande, Rio de Janeiro

Abstract

The existence of a persistent circulation between the western and eastern Ilha Grande Bay (IGB) portions, through the Ilha Grande Channel (IGC), was reported in the 1970s' to 1990s' papers, which the analyzed time series did not exceed 30 days. The data time-range limitation did not allow past studies to address the IGC eastward current's permanent or semipermanent character. In addition to the temporal character, there is no consensus regarding the mechanisms responsible for this current. The horizontal density gradient and the barotropic pressure gradient, both internally established, between the western and eastern IGB portions were speculated. In this context, the present work analyzed a continuous time series, recorded in 1998 and 1999, containing more than 15 months of sea-level rise, current, and temperature data measured at a depth of 12m on the terminal pier. of oil from TEBIG (Petrobras), located at CIG. Thus, the investigated current has a permanent temporal character, considering the 15 months analyzed, with an average eastward velocity of 6.90 cm.s-1. Furthermore, highresolution three-dimensional numerical experiments covering the entire Southeast Continental Shelf (SEPC) until the Ilha Grande and Sepetiba Bays interior were conducted. The IGC current was related to a subsurface coastal current, which makes up the continental branch of a cyclonic circulation cell over the South Brazil Bight, caused by the shelf density field adjustment. Finally, the first empirical mode accounted for 96% of the along-channel current variance and was related to circulation caused by density gradients outside the IGB. The second mode accounted for 2% of the total variance and was associated with the IGB adjacent shelf winds.