Wind-Driven oscillations in the meridional overturning circulation near the equator. Part I: Numerical models

The great ocean conveyor presents a time-mean perspective on the interconnected network of major ocean currents. Zonally integrating the meridional velocities, either globally or across basin-scale domains, reduces the conveyor to a 2D projection widely known as the meridional overturning circulation (MOC). Recent model studies have shown the MOC to exhibit variability on near-inertial time scales, and also indicate a region of enhanced variability on the equator. We present an analysis of three integrations of a global configuration of a numerical ocean model, which show very large amplitude oscillations in the MOCs in the Atlantic, Indian, and Pacific Oceans confined to the equatorial region. The amplitude of these oscillations is proportional to the width of the ocean basin, typically about 100 (200) Sv (1 Sv ≡ 106 m3 s−1) in the Atlantic (Pacific). We show that these oscillations are driven by surface winds within 10°N/S of the equator, and their periods (typically 4–10 days) correspond to a small number of low-mode equatorially trapped planetary waves. Furthermore, the oscillations can be well reproduced by idealized wind-driven simulations linearized about a state of rest.