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The oceanic circulation entering the tropical southwest Pacific (SWP) is dominated by the broad westward flow of the South Equatorial Current (SEC), which is forced by the trade winds. It has been argued that the numerous islands of the SWP are able to restructure the SEC into a series of deep and narrow zonal jets, which control important pathways connecting equatorial and extraequatorial signals. The primary objective of this paper is to improve the understanding of the structure and dynamics of SWP zonal jets, giving special attention to topographic effects. This study is based on the use of a high-resolution regional oceanic model, whose solution is compared with observations, as well as with solutions from global models and the Sverdrup relation. The model used here indicates that the regional topography drives a general equatorward shift of the SEC, which is beneficial to the North Fiji, North Vanuatu, and North Caledonian jets. A depth-integrated vorticity budget shows that this topographic effect is considerably attenuated by baroclinicity and advection processes, but not to the point of total compensation as often admitted for the interior ocean. The effect of nonlinear advection is to allow flow rectification of the jets fluctuations, taking the form of zonally elongated dipole circulations in the leeward side of the islands.

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We describe the seasonal cycle of the alongshore flows on the Northwestern Iberian Margin and explain what are the important mechanisms forcing the system. We used a 20-year model simulation at 2.3 km horizontal resolution, with realistic atmospheric forcing and covering the whole Western Iberian Margin. The model results are compared with satellite data, with data measured at two moored buoys and with a compilation of current meter data available for the study region. We show that currents over the slope are divided in three different cores: the Iberian Poleward Current (IPC) occupying the top 350 m, a deeper core at Mediterranean Water levels (∼600-1200 m) and in between the two, an equatorward core centered just beneath the IPC core, the Upper Slope Countercurrent (USCC). The IPC is present almost yearlong, including in summer months, when it is close to the shelf-break and topped by the equatorward upwelling jet. After September, the IPC intensifies and its core surfaces. Heat and salinity budgets on the shelf and slope are dominated by advection, confirming the important role of the IPC in driving the temperature and salinity seasonal cycles. Analysis of the seasonal cycle of the barotropic vorticity equation on the slope, shows that the main forcing mechanism of northward flows is the "Joint Effect of Baroclinicity and Relief" (JEBAR), whose contribution is higher in summer than in winter. In December and January, when the IPC is stronger and surface intensified, the main contribution is from southerly winds.The cross-shore analysis of these terms shows that JEBAR decreases substantially at the core of the IPC because, as advection terms become important, the northward density flux diminishes the local meridional density gradients, resulting in the decrease of JEBAR in the months of strong IPC. Ocean-atmosphere system 2009). Pingree and Le Cann (1992a) named this warm water intrusion in the north coast as Navidad, because it occurs near Christmas. Fig. 1 (right) shows the average January SST, with warm waters over the shelf and slope, and with a representation of a schematic IPC. At intermediate levels (∼800-1200 m), the water also circulates poleward along the western Iberian slope, transporting the 20 warm and saline Mediterranean Water (Daniault et al., 1994; Ambar and Fiúza, driving the temperature and salinity seasonal variability? And finally, 4) What are the main forcings of the IPC and how do they vary seasonally? In the next section, we present a description of the numerical model, the observed data, the model configuration details and the comparison of model results with the observations. In section 3, we present the model results. In 50 section 4, we analyze the vorticity balances. Section 5 is the discussion and comparison with previous studies of the region and section 6, the summary and 3 conclusions. 2. Model, configuration and observed data 2.1. Model 55 The Regional Ocean Modeling System (ROMS), is a primitive equation, hydrostatic, sigma coordinate, free-surface ocean model (Shchepetkin an...