On the temporal variability of the Sea Surface Temperature on the Tropical Southwest Atlantic Continental Shelf

In this study, we used 29 years of daily 4-km AVHRR Pathfinder Version 5.2 (PFV5.2) data to study the SST temporal variability over the continental shelf in the Southwestern Tropical Atlantic Ocean (SWTA) (1 to 6 degrees S and 41 to 35 W). Firstly, we evaluated the cloud cover and assessed the annual and semi-annual deterministic signals using a harmonic analysis. The annual plus the semi-annual cycles were removed from the original data and a low-pass filter was used to estimate the contribution of the inter-annual component. Finally, the inter-annual signal was also removed and the variance associated to the remaining residuals was calculated to address the intra-annual component. We show that the region is covered by clouds and SST data unavailable - between 40% and 60% of the time. The annual signal explains most of the variability over the area with a coefficient of determination higher than 70% and amplitudes ranging from 1 to 1.5 degrees C. The amplitudes increase eastwards and towards the coast. The phase of the annual cycle presents values between 40 and 60 days with respect to the 1st of January, occurring earlier over the eastern continental shelf. The semi-annual signals present amplitudes close 0.5 degrees C in most of the region decreasing towards offshore regions. The continental shelf as whole, experienced weak inter-annual variability with variance values around 0.2 degrees C. After the annual and semi-annual signals were removed, the inter-annual signal explains 30-45 % of the residual. The intra-annual variability presents variance values between 0.2 and 0.3 degrees C and explains most of the residual variability. Both inter and intra-annual SST variability in the SWTA is spatially homogenous. For the first time, the SST temporal variability ranging from sub-seasonal to inter-annual was addressed in the SWTA continental shelf region. In light of the results, we have showed that the SST in the Tropical Southwest Atlantic continental shelf presents a small temporal and spatial variability. Most of the SST is explained by the annual cycle followed by the intra-annual variations.