Eddy-induced meridional transport variability at ocean western boundary

Meridional transport variability induced by westward-propagating eddies impinging on the western boundary is investigated both analytically and numerically. A simple theory is first developed in the framework of the reduced-gravity model which relates eddy-induced meridional transport to eddy thickness anomalies propagated into the western boundary by long Rossby waves, and this is followed by a suite of numerical model experiments. It is found that eddies impinging on the western boundary excite boundary waves that propagate equatorward along the western boundary, which leads to coherent meridional overturning circulation (MOC) anomalies equatorward of the incident eddy field. The magnitude and duration of eddy-induced MOC anomalies are variable and irregular, ranging from less than 1 Sv to over 5 Sv and from less than 10 days to over 100 days. Importantly, these eddy-induced MOC anomalies lead to considerable meridional heat transport variability across the latitudes, with implications for seasonal and interannual climate variability and prediction.