PIRATA velocity observations from moorings, cruises, and complementary platforms (ADCPs, drifters, Argo) have provided unprecedented insights into tropical Atlantic circulation and its forcing. Long-term records at 23°W, 10°W, and 0°E showed that the Equatorial Undercurrent (EUC) seasonal cycle arises from resonant equatorial basin modes rather than local winds, with transport maxima in boreal spring and fall (Brandt et al., 2016). PIRATA also clarified the termination of the EUC in the Gulf of Guinea and its impact on salinity and SST variability during the Atlantic Cold Tongue season (Da-Allada et al., 2017; Kolodziejczyk et al., 2014). On interannual timescales, EUC transport anomalies were linked to Atlantic Niño events, distinguishing between wind-driven and advection-driven mechanisms (Brandt et al., 2014). PIRATA cruises further documented regional features such as the Guiana Undercurrent and the role of subtropical cells in redistributing Amazon plume freshwater (Foltz et al., 2015; Herbert et al., 2016). Finally, PIRATA data have been key to characterizing intraseasonal variability, including tropical instability waves, which modulate heat and salt budgets and drive equatorial circulation (Grodsky et al., 2005; Hummels et al., 2013; Wenegrat & McPhaden, 2015).
