Preprints
https://doi.org/10.5194/gmd-2021-436
https://doi.org/10.5194/gmd-2021-436

Submitted as: model experiment description paper 10 Jan 2022

Submitted as: model experiment description paper | 10 Jan 2022

Review status: this preprint is currently under review for the journal GMD.

The bulk parameterizations of turbulent air-sea fluxes in NEMO4: the origin of Sea Surface Temperature differences in a global model study

Giulia Bonino1, Doroteaciro Iovino1, Laurent Brodeau2, and Simona Masina1 Giulia Bonino et al.
  • 1Ocean Modeling and Data Assimilation Division, Centro Euro-Mediterraneo sui Cambiamenti Climatici, Bologna, Italy
  • 2Centre National de la Recherche Scientifique, IGE/MEOM, Grenoble, France

Abstract. Wind stress and turbulent heat fluxes are the major driving forces which modify the ocean dynamics and thermodynamics. In the NEMO ocean general circulation model, these turbulent air-sea fluxes (TASFs), which are components of the ocean model boundary conditions, can critically impact the simulated ocean characteristics. This paper investigates how the different bulk parametrizations to calculated turbulent air-sea fluxes in the NEMO4 (revision 12957) drives substantial differences in sea surface temperature (SST). Specifically, we study the contribution of different aspects and assumptions of the bulk parametrizations in driving the SST differences in NEMO global model configuration at ¼ degree of horizontal resolution. These include the use of the skin temperature instead of the bulk SST in the computation of turbulent heat flux components, the estimation of wind stress and the estimation of turbulent heat flux components which vary in each parametrization due to the different computation of the bulk transfer coefficients. The analysis of a set of short-term sensitivity experiments, where the only experimental change is related to one of the aspects of the bulk parametrizations, shows that parametrization-related SST differences are primarily sensitive to the wind stress differences across parametrizations and to the implementation of skin temperature in the computation of turbulent heat flux components. Moreover, in order to highlight the role of SST-turbulent heat flux negative feedback at play in ocean simulations, we compare the TASFs differences obtained using NEMO ocean model with the estimations from Brodeau et al. (2017), who compared the different bulk parametrizations using prescribed SST. Our estimations of turbulent heat flux differences between bulk parametrizations is weaker with respect to Brodeau et al. (2017) differences estimations.

Giulia Bonino et al.

Status: open (until 07 Mar 2022)

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Giulia Bonino et al.

Giulia Bonino et al.

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Short summary
The sea surface temperature (SST) is highly influenced by the transfer of energy driven by turbulent air–sea fluxes (TASFs). In NEMO ocean general circulation model, TASFs, are computed by means of bulk formulas. Bulk formulas requires the choice of a given bulk parameterization, which influences the magnitude of the TASFs. Our results show that parametrization-related SST differences are primarily sensitive to the wind stress differences across parametrizations.