Internal variability of the tropical Atlantic ocean

A 100 year integration of an eddy resolving numerical model of the tropical Atlantic is analyzed to quantify the interannual variability caused by internal variability of ocean dynamics. It is found that, except for the spring position of the SST maximum, the strength of internal variability in the tropical Atlantic is comparable to published mid-latitude values but is dwarfed by the strength of the seasonal cycle. During spring however, the equatorial meridional SST gradient is very weak, and internal oceanic variability causes a variability in the position of the SST maximum that is comparable to its observed variability. It is shown that these variations in the SST are due to tropical instability waves whose strength varies from year to year, even under climatological forcing. The results suggest that in winter, the predictability of the location of the tropical SST maximum is limited to the persistence time of SST anomalies which is approximately 100 days.