On the harmonic constants of tides and tidal currents of the South-eastern brazilian shelf

Abstract

Series of sea-level heights from three permanent coastal stations, and sea-surface heights and currents from three non-permanent pelagic sites, in the South-eastern Brazilian shelf, were subjected to tidal analysis by the harmonic and response methods, in order to determine their tidal constants. Semi-diurnal heights constituents M 2 and S 2 have a clockwise propagation in the southern part of the area and a counterclockwise one in the northern part. Their amplitudes show a general increase from east to west, being higher near the port of Paranaguá, and then decrease further south. Among the diurnals, Q 1 and O 1, propagate from west to east in a clockwise propagation, while the K 1 and P 1 propagations approximately follow the semi-diurnals components and also have higher amplitudes near Paranaguá Cananéia, propagating clockwise in the southern part of the area and counterclockwise in the northernmost one. The M 3 has higher amplitudes, as the semi-diurnals, along the Paranaguá shelf compared to the other stations. The phases of M 3 from the shelf values also seem to indicate a double sense of propagation in the area. The diurnal current components O 1 and K 1 have greater amplitudes at the surface layers (major axes of tidal ellipses with 7.5 and 11.2 cm/s in the northern part of the shelf) and tend to become smaller with depth, with their ellipses axes rotating counterclockwise from surface to the bottom. The semi-diurnal current components M 2 and S 2 have, in each station, approximately similar amplitudes and nearly the same ellipses orientation, along the vertical profiles (major axes at the surface with 7.3 and 4.1 cm/s in the southern part of the shelf); these features are also followed by M 3 (this current constituent was quite uniform in the whole area and only the ellipses orientation varied significantly). Most of the tidal currents are counterclockwise from surface to the bottom and are seen to be affected by the bathymetry and displacements of water masses present in the area–shelf water (SW) at the surface, tropical water (TW) at mid column and sub-tropical water (STW) at the bottom layer. Prevailing winds and inertial motions also affect the constituents of tides and tidal currents in the study area.