On the dynamics of the slope current system along the west European margin. Part I: Analytical calculations and numerical simulations with steady-state forcing

The dynamics of the baroclinic slope current system along the western European margin in the Bay of Biscay and along the northern Iberian Peninsula are investigated in two different models, one analytical and one numerical. Investigated here is the hypothesis that the steady-state slope current system is driven by the large-scale meridional density gradients. An analysis of the observed density fields evidences a four-layer structure with meridional gradients of alternate signs, which is also found in the numerical model. The linear analytical model of the continental margin shows that such a density structure is enough to obtain a steady-state four-layer slope current system comparable to the observed annual mean circulation. The slope currents result from a balance between bottom friction and meridional density gradients. The numerical simulation with an ocean general circulation model forced only by the large-scale density gradients at the lateral boundaries presents a four-layer slope current system similar to the circulation obtained in the analytical model. The study confirms that the large-scale meridional density gradients are the main driving mechanism for the steady-state slope current system; the large seasonality of these currents, however, requires a more extended model, which is discussed in a companion paper (Part II). © 2008 American Meteorological Society.