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Variability of the Atlantic Ocean North Equatorial Counter Current from 15 years of ADCP Observations and GLORYS12V1 Reanalysis
  • Djoirka Minto Dimoune,
  • Fabrice Hernandez,
  • Moacyr Araujo
Djoirka Minto Dimoune
Universidade Federal do Pernambuco

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Fabrice Hernandez
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Moacyr Araujo
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Ocean current observations from different seasons of 15 years of vessel-mounted Doppler Current Profiler, merely from the PIRATA program, and drifters-derived near-surface currents are used to describe the structure, the variability of the North Equatorial Countercurrent (NECC) at 38{degree sign}W in the tropical Atlantic. Then used to validate the GLORYS12V1 ocean reanalysis, showing that the inferred NECC’s characteristics present reliable realism. This allows further analysis of the NECC’s seasonal and interannual variabilities over the full reanalysis period (1993-2018). The NECC presents an annual cycle of northward migration driven by the wind field with a two-cores structure. It exhibits a single branch, the sNECC, from December to June. With the addition of a second branch, the nNECC, the rest of the year. The sNECC starts the seasonal cycle in June, then grows northward, driven by the northward migration of the ITCZ with a three-month time lag. The nNECC core appears in August, migrates northward, then vanishes in December/January around 12{degree sign}N. From January to May the sNECC decays, with northward displacement toward 7-9{degree sign}N, driven by the second zero of the wind stress curl. From year to year, the NECC shows significant variations in relation with the tropical Atlantic zonal and meridional climate modes. First, positive NECC transport anomalies appear with “warm” meridional mode and zonal mode “Atlantic Niña” phases. Second, positive anomalies appear with weak meridional “cold” phase, and “Atlantic Niño” increasing zonal mode. Third, negative NECC anomalies occur with “cold” meridional phase and a negative zonal mode.