Investigating of the two-core structure of the Atlantic North Equatorial Countercurrent with the GLORYS12V1 reanalysis

Abstract

Twenty-six years of the high-resolution global ocean reanalysis GLORYS12V1 are used to investigate the temporal and spatial variability of the two-core structure of the North Equatorial Counter Current (NECC) in the western and central tropical Atlantic. The two cores of the NECC exhibit mean positions of 6.3°N±1.4° and 9.7°N±1°, and of 5.4°N±1.1° and 8.9°N±0.9° respectively in the area west of 32°W and in the area between 32°W and 22°W. Both areas witness a semi-annual cycle of the position of the southern core with northernmost positions respectively in May and July, and in March and July. The transport of the branch associated to the southern cores shows annual cycles with maxima occurring in August (>17 Sv) and July (>7 Sv) respectively in the western and central areas. The annual cycle in the West is influenced by the wind stress curl (WSC) strength. The central area might be influenced by a return flow of the northern branch of the South Equatorial Current over the central Atlantic. At the opposite, the transport associated with the NECC’s northern core shows the same annual cycles with maxima occurring in September in both areas. This transport of the NECC shows seasonal cycles leaded by the WSC strength with 1-month lag. 83% and 71% of the total transport between the first 150 m-depth is above the thermocline respectively in the western and central areas. In the West, the northern core transport shows year-to-year variations associated with the WSC strength, while the southern core position of the NECC in the central tropical Atlantic appears influenced by the InterTropical Convergence Zone migration.