Upper-Ocean Circulation and Tropical Atlantic Interannual Modes

The impact of tropical Atlantic Ocean variability modes in the variability of the upper-ocean circulation has been investigated. For this purpose, we use three oceanic reanalyses, an interannual forced-ocean simulation, and satel-lite data for the period 1982-2018. We have explored the changes in the main surface and subsurface ocean currents during the emergence of Atlantic meridional mode (AMM), Atlantic zonal mode (AZM), and AMM-AZM connection. The de-veloping phase of the AMM is associated with a boreal spring intensification of North Equatorial Countercurrent (NECC) and a reinforced summer Eastern Equatorial Undercurrent (EEUC) and north South Equatorial Current (nSEC). During the decaying phase, the reduction of the wind forcing and zonal sea surface height gradient produces a weakening of sur-face circulation. For the connected AMM-AZM, in addition to the intensified NECC, EEUC, and nSEC in spring, an anomalous north-equatorial wind curl excites an oceanic Rossby wave (RW) that is boundary-reflected into an equatorial Kelvin wave (KW). The KW reverses the thermocline slope, weakening the nSEC and EUC in boreal summer and au-tumn, respectively. During the developing spring phase of the AZM, the nSEC is considerably reduced with no consistent impact at subsurface levels. During the autumn decaying phase, the upwelling RW-reflected mechanism is activated, modi-fying the zonal pressure gradient that intensifies the nSEC. The NECC is reduced in boreal spring-summer. Our results re-veal a robust alteration of the upper-ocean circulation during AMM, AZM, and AMM-AZM, highlighting the decisive role of ocean waves in connecting the tropical and equatorial ocean transport.

Automated summary

The study investigates the impact of tropical Atlantic Ocean variability modes on the variability of the upper-ocean circulation. Multiple datasets including oceanic reanalyses, simulations, and satellite data were utilized for the period 1982-2018. The results reveal significant changes in the surface and subsurface ocean currents during the emergence of Atlantic meridional mode (AMM), Atlantic zonal mode (AZM), and the connection between AMM and AZM. Ocean waves play a crucial role in connecting tropical and equatorial ocean transport.