Assessment of Santa Catarina shelf currents through the analysis of indirect measurements

Abstract

Preliminary analyses on the use of drift measurements of a buoy in the study of shelf currents are presented. The equipment was moored at Santa Catarina Shelf in Southern Brazil. The drift was measured by means of a GPS which provided buoy's geographical coordinates on an hourly basis. The data was decomposed in meridional and zonal position components and along with wind and sea level data, covered a period of 203 days from late summer (March 21 ) to late spring (October 11 ) of 2002. Statistical comparison between mean sea level (msl) and the meridional buoy positioning displayed very high correlation (R =0.83) with a 3 h delay in relation to msl. The best correlation between meridional wind and buoy's drift was attained at 10 h time lag (R =0.63). Sea level analysis characterizes the tide as mixed, mainly semidiurnal. Diurnal and Semi-Diurnal bands accounted for 63.6% of energy spectra in comparison to 36.4% on the Meteorological-forcing band. Low frequency signal in Meteorological band were clearly dominant in the buoy's meridional series, accounting for 90% of energy spectra. The buoy mooring system seems to work as a very useful indicator of the sense of geostrophic currents over the shelf, which seems to respond to both regional as well remote wind forcing.