Contribution of the wind, Loop Current Eddies, and topography to the circulation in the southern Gulf of Mexico

Abstract The Bay of Campeche, located in the southern Gulf of Mexico (GoM), is characterized by a semi-permanent cyclonic circulation commonly referred to as the Campeche Gyre (CG). Several studies documenting its upper layer structure have suggested a possible relationship between its seasonal variability and the wind stress, and that non-seasonal variability arises mainly from the interaction of the gyre with Loop Current Eddies (LCEs) that arrive in the region. Nevertheless, a partition of the contributions of these forcings to the circulation of the CG in a statistically consistent manner is still needed. This study examines the wind- and eddy-driven circulation with long-term numerical simulations of the GoM using the HYbrid Coordinate Ocean Model. Our results show that, in the absence of LCEs, the wind can sustain a seasonal-modulated circulation in the CG, confined within the upper 600 m. When considering LCEs, high fluctuations on the flow at intraseasonal time scales are imposed. We found that the LCEs influence the western Bay of Campeche circulation through two main mechanisms: (a) by decelerating and inhibiting the CG through a positive vorticity flux out of the bay, leading to reversals in the flow if LCE southward penetration is large, or (b) by strengthening the CG when a big cyclone, accompanying the LCE, enters the region. It is proposed that the second mechanism is responsible for inducing a net weak cyclonic circulation in the Bay in the absence of wind. Furthermore, past studies have shown that the CG behaves as an equivalent-barotropic flow, with topography acting to confine the CG to the west of the bay. In our modeling results, the role of topography manifests similarly among the different numerical experiments, resulting in closed geostrophic contours to the west of the bay that confine an upper-layer, nearly-symmetric, equivalent-barotropic CG.