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

Abstract

[1] 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.

Sensitivity of near-surface Tropical Instability Waves to submonthly wind forcing in the tropical Atlantic

“…Satellite images as well as in situ observations in temperature, zonal and meridional currents have documented the principal characteristics of TIWs in the Atlantic (e.g. Düing et al, 1975;Qiao and Weisberg, 1995;Wainer et al, 2003;Caltabiano et al, 2005;Bunge et al, 2006Bunge et al, , 2007Athié and Marin, 2008). They have periods between 20 and 50 days, wavelengths of 700-1200km and westward phase velocities of 30-60 cm/s.…”

“…Those signals have been observed principally from time series of velocity and temperature at a few mooring sites along the equator (Garzoli, 1987;Wainer et al, 2003;Bunge et al, 2006), but also away from the equator along 3°N and 9°N (Garzoli, 1987). Unfortunately, the temporal resolution of satellite observations is insufficient to study the spatial distribution of the surface variability in detail at those frequencies in the ocean, both for SST and sea level anomalies.…”

Equatorial currents transport changes for extreme warm and cold events in the Atlantic Ocean

“…With respect to sea surface temperature (SST), the tropical Atlantic ocean displays two dominant modes of interanual variability largely described in the literature [e.g. Servain , 1991; Wainer et al , 2002; Servain et al , 2002]. One represents an inter‐hemispheric SST gradient signature.…”

SST spatial anisotropic covariances from METOP-AVHRR data

“…Wainer et al (2003)) and from remote sensing sources (cf. Tandeo et al (2011)) but, its spatial variability, especially spatial anisotropy and non-stationarity, remains poorly explored.…”