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Large-scale ocean circulation, dynamics, and air-sea exchanges : Argo observations of the mean and time- varying ocean

  • Author(s): Giglio, Donata
  • et al.
Abstract

The large-scale ocean circulation, dynamics, and air-sea exchanges are investigated, based on observational datasets including Argo and satellite altimetry, and viewed in the framework of modern theoretical ideas. Initially, the wind-driven interannual variability of the subtropical North Pacific is described. Using the extensive Argo dataset, it is seen that the North Pacific gyre varies in the strength of its interior circulation and in its spatial orientation, on interannual timescales. Also, satellite altimetry shows variations in sea surface height that are consistent with Argo steric height changes, and enabled a temporal extension of the 2004-2011 Argo study back to 1993. The next part of the thesis is focused on annual steric variability, including diabatic changes in the surface layer due to air-sea buoyancy fluxes and adiabatic changes due to wind-forced advection, which are dominant in the subsurface ocean. The annual signal in subsurface (200-2000 db) steric height zonally averaged over a season shows good agreement with the wind-forced vertical advection contribution, both in the global ocean and in different basins. This study, the first on global scale, also shows that the annual vertical advection extends deep into the water column. Next, the global pattern of climatological monthly heat and freshwater fluxes at the ocean surface is estimated using Argo temperature and salinity profile data for the period 2004 to 2013. The air-sea flux estimates from Argo are described in global maps and basin-wide integrals, in comparison to atmospheric reanalysis data and to air-sea flux products based on observations. This ocean-based estimate of surface fluxes is consistent with property variations in the subsurface ocean and indicates greater amplitude for the climatological monthly heat flux values in the subtropics compared to other products. Similarly, the combination of Argo freshwater flux and reanalysis evaporation, suggests greater amplitude for climatological monthly precipitation in the tropics. Finally, this thesis describes the mean field of the North Pacific subtropical gyre using Argo T/S and trajectory data. The gyre is deeper than 1975 db and than the densest ventilated isopycnal, and it is deepest in the northwest subtropics. In the east, its axis tilts northeast with increasing pressure

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