Interaction between the Atlantic meridional and Nino modes

Interaction between the tropical Atlantic meridional and Nino modes is investigated using observations and a quasi-analytical linear equatorial ocean wave model. It is found that equatorial zonal wind stress anomalies associated with the boreal spring meridional mode generate eastward propagating equatorial Kelvin waves in the central and eastern Atlantic Ocean, where variability associated with the Nino mode is strongest. These same wind stress anomalies force westward propagating equatorial Rossby waves that reflect at the western boundary into eastward propagating Kelvin waves during boreal spring and summer. The boundary-generated Kelvin waves are of the opposite sign to those directly forced by the winds earlier in the spring, so they tend to damp the Nino mode during boreal summer. The interaction between the boreal spring meridional mode and the summer Nino is therefore mediated by directly wind-forced equatorial Kelvin waves and the delayed negative feedback from western boundary reflections of wind-forced Rossby waves.