Influence of mesoscale atmospheric forcing on mean sea level at Piraquara, RJ

Abstract

The work refers to variations of the mean sea level (MSL) in Piraquara (RJ) due to mesoscale atmospheric disturbances in the South and Southeast Brazil oceanic area. The sea level data were submitted to a verification and consistence process, and then they were validated with the help of predicted levels by the software Pacmaré (FRANCO, 1992). For the pressure and wind velocities, the NCEP re-analysis data was used. Thompson's low pass optimizable filter was used to remove high frequencies in the data. Differently to the habitual use of quarters of year in climatologic studies, in this work partitions of the year centered in solstice and equinox were considered. About the results of the statistical analysis in the time domain, it was seen that MSL response has time delays with respect to atmospheric pressure and wind stress. The spectral analysis, in the frequency domain showed that during the equinox centered days the high peaks of energy are in relatively lower frequencies than in the solstice period, and they appear in the same frequency band as that of the cold fronts. Pressure points under continental influences present little coherent with the MSL variations in Piraquara, on the other hand, the effects of the longitudinal component to the coast are very well-known on the mean sea level. It is proposed to study the subtropical anticyclone in the South Atlantic Ocean in order to identify probable phenomena that explain the occurrence of high energy picks in low frequencies, as well as identify types of cold fronts which reach South and Southeast regions of Brazil, since they have diferente impacts on the coastal region.