Development of a feature-oriented regional modelling system for the North Brazil Undercurrent region (1°–11°S) and its application to a process study on the genesis of the Potiguar Eddy

Abstract

Key elements of a Feature-oriented regional modelling system (FORMS) in the Western Equatorial Atlantic (1°–11°S) are developed for possible application in an operational forecast system as well as in process-oriented studies. This equatorial margin region is dominated by the northwestward flowing near surface North Brazil Undercurrent (NBUC) and the southeastward Deep Western Boundary Current (DWBC). Specifically, we investigate the genesis of a subsurface frontal meander of the NBUC, centred at about 4°S, 36.5°W, called the Potiguar Eddy (PE). The Feature Models (FMs) of NBUC and DWBC are first developed from observed velocity data, with temperature calculated through the thermal wind equation, and salinity from climatology. Two numerical experiments were then set up for the process study, (i) a realistic NBUC + DWBC experiment, with maximum depth of 5500 m, and (ii) a NBUC-only experiment, with maximum depth limited to 1500 m. Results conclude that the PE can be generated by a velocity field containing only the NBUC, and the DWBC–induced vertical shear seems to play a part on the eddy’s baroclinic characteristics (vertical extent and strength). This study highlights the potential of applicability of FORMS for operational forecasts and for process studies in similar regions of the world ocean where currents and topography interact to create permanent and/or semi-permanent eddies.