16 Nov 2022
16 Nov 2022
Status: this preprint is open for discussion.

Joint observation-model mixed-layer heat and salt budgets in the eastern tropical Atlantic

Roy Dorgeless Ngakala1,2, Gael Alory3, Casimir Yélognissè Da-Allada1,4,5, Olivia Estelle Kom1, Julien Jouanno3, Willi Rath6, and Ezinvi Baloïtcha2 Roy Dorgeless Ngakala et al.
  • 1Department of Oceanography and Applications, International Chair in Mathematical Physics and Applications, University of Abomey-Calavi, Cotonou, Benin
  • 2Department of Oceanography and Environment, Institut National de Recherche en Sciences Exactes et Naturelles, Pointe-Noire, Congo
  • 3Laboratoire d’Etudes en Géophysique et Océanographie Spatiales, University of Toulouse, Toulouse, France
  • 4Laboratoire de Géosciences, de l’Environnement et Applications, Université Nationale des Sciences Technologies, Ingénierie et Mathématiques, Abomey, Benin
  • 5Laboratoire d’Hydrologie Marine et Côtière, Institut de Recherches Halieutiques et Océanologiques du Bénin, Cotonou, Benin
  • 6GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel, Germany

Abstract. In this study, we use a joint observation-model approach to investigate the mixed-layer heat and salt annual mean and seasonal budgets in the eastern tropical Atlantic. The regional PREFCLIM observational climatology provides the budget terms with a relatively low spatial and temporal resolution compared to the online NEMO model, and this later is then re-sampled as in PREFCLIM climatology. In addition, advection terms are recomputed offline from the model as PREFCLIM gridded advection computation. In Senegal, Angola and Benguela regions, the seasonal cycle of mixed-layer temperature is mainly governed by surface heat fluxes; however, it is essentially driven by vertical heat diffusion in Equatorial region. The seasonal cycle of mixed-layer salinity is largely controlled by freshwater flux in Senegal and Benguela regions; however, it follows the variability of zonal and meridional salt advection in Equatorial and Angola regions respectively. Our results show that the time-averaged spatial distribution of NEMO offline heat/salt advection terms compares much better to PREFCLIM horizontal advection terms than the online heat/salt advection terms. However, the seasonal cycle of horizontal advection in selected regions shows that NEMO offline terms do not always compare well with PREFCLIM, sometimes less than online terms. Despite this difference, these results suggest the important role of small scale variability in mixed-layer heat and salt budgets.

Roy Dorgeless Ngakala et al.

Status: open (until 11 Jan 2023)

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Roy Dorgeless Ngakala et al.

Roy Dorgeless Ngakala et al.


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Short summary
Surface heat flux is the main driver of the heat budget in the Senegal, Angola and Benguela regions, but not in the Equatorial region. In the Senegal and Benguela regions, freshwater flux governs the salt budget while in Equatorial and Angola regions, oceanic processes are the main drivers. Results from numerical simulation show the important role of mesoscale advection for temperature and salinity variations in the mixed-layer. Non-linear processes unresolved by observations play a key role.