Salinity’s Role in Tropical Atlantic Instability Waves - A Unique Vantage Point from Aquarius/SAC-D
[13-Nov-2013] Lee, T., Lagerloef, G., McPhaden, M., Willis, J., and Gierach, M.
Presented at the 2013 Aquarius/SAC-D Science Team Meeting
Tropical Atlantic instability waves (TIWs) play an important role in the dynamics of the tropical Atlantic Ocean and related climate variability. Previous studies suggest that the sea surface temperature (SST) signature of these waves are strongest in the eastern-central equatorial Atlantic (around 15W). Our analysis of Aquarius sea surface salinity (SSS) shows that these waves remain strong in the western part of the basin, which is in stark contrast to SST. This is because of the perturbation to the large meridional gradient of salinity between the salty South Atlantic water and the fresher water associated with the extension of the Amazon plume. A previous energetic analysis of the TIWs in the central equatorial Atlantic (23W) using limited mooring observations and auxiliary data suggested the importance of salinity variation in TIW-related baroclinic energy conversion rate at that location. Our analysis across the entire equatorial Atlantic indicates that the contribution of salinity to the perturbation potential energy (PPE) increases substantially from the eastern to the western basin. Our analysis also suggests that the effect of salinity on PPE includes the direct salinity effect and an indirect effect, a substantial re-enforcement by the co-variability between salinity and temperature fluctuations.