Time scales of upper ocean temperature variability inferred from the PIRATA data (1997-2000)

Abstract

Time series from the PIRATA 10-minute measurements are investigated in order to study the upper-ocean thermal field time-scales of variability using the serial covariance power spectra method and wavelet analysis. This is one of the few studies that analyze in time and space the PIRATA buoy data in the region. Analysis of the depth of the 20°C isotherm show distinct patterns for the northwestern Atlantic at 8N-38W and the southeastern Atlantic, at 10S-10W. In the west, warm surface waters are accompanied by a shallower thermocline while in the east warm surface waters are associated with its deepening, consistent with Houghton [1991]. At higher frequencies the dominant signals in sea surface temperature are the diurnal and semi-diurnal cycles. Spectral analysis of the depth of the 20°C isotherm show a predominance of the semi-diurnal period. In the eastern Atlantic there are two additional dominant bands in the spectra: 10-14 days, 25-27 days and for the depth of the 20°C isotherm there is also a lower frequency band at 20-40 days associated with tropical instability waves at the equator. The first band can be associated with atmospherically forced motions and the lower frequency band with barotropic instability waves.