Recipes for How to Force Oceanic Model Dynamics

Abstract

The current feedback to the atmosphere (CFB) contributes to the oceanic circulation by damping eddies. In an ocean‐atmosphere coupled model, CFB can be correctly accounted for by using the wind relative to the oceanic current. However, its implementation in a forced oceanic model is less straightforward as CFB also enhances the 10‐m wind. Wind products based on observations have seen real currents that will not necessarily correspond to model currents, whereas meteorological reanalyses often neglect surface currents or use surface currents that, again, will differ from the surface currents of the forced oceanic simulation. In this study, we use a set of quasi‐global oceanic simulations, coupled or not with the atmosphere, to (i) quantify the error associated with the different existing strategies of forcing an oceanic model, (ii) test different parameterizations of the CFB, and (iii) propose the best strategy to account for CFB in forced oceanic simulation. We show that scatterometer wind or stress are not suitable to properly represent the CFB in forced oceanic simulation. We furthermore demonstrate that a parameterization of CFB based on a wind‐predicted coupling coefficient between the surface current and the stress allows us to reproduce the main characteristics of a coupled simulation. Such a parameterization can be used with any forcing set, including future coupled reanalyses, assuming that the associated oceanic surface currents are known. A further assessment of the thermal feedback of the surface wind in response to oceanic surface temperature gradients shows a weak forcing effect on oceanic currents.

Atmospheric-Driven and Intrinsic Interannual-to-Decadal Variability in the Kuroshio Extension Jet and Eddy Activities

“…As the satellites observe sea surface wind speeds relative to the surface ocean currents, the OGCM double counts the effect of the surface currents (Zhai and Greatbatch, 2007). Furthermore, the OGCM is driven by the atmospheric reanalysis field that does not include responses to the modeled SST variability, and could underestimate the western boundary currents and associated eddy activities (Renault et al, 2019(Renault et al, , 2020. Sasaki et al (2020) shows further details of the model setup and comparisons between observations and modeled fields in OFES2.…”

Impact of horizontal resolution on global ocean–sea ice model simulations based on the experimental protocols of the Ocean Model Intercomparison Project phase 2 (OMIP-2)

“…However, the use of absolute wind in FSU-HYCOM is not sufficient to raise the level of surface variability to that of the observations, and Chassignet and Xu (2017) argue that one actually needs to significantly increase the resolution (∼ 0.01 • ) in order to resolve the submesoscale instabilities that can energize the mesoscale (Callies et al, 2016) and therefore enhance eddy kinetic energy comparable to the mesoscale AVISO observations. It is more physical to take into account the vertical shear between atmospheric winds and ocean currents when computing the wind stress (see Renault et al, 2020, for a review) as it allows for a better representation of western boundary current systems (Ma et al, 2016), especially the Agulhas Current retroflection and associated eddies (Renault et al, 2017). In FSU-HYCOM, which uses absolute wind, the Agulhas eddies are too regular and follow the same pathway.…”

Impact of horizontal resolution on global ocean-sea-ice model simulations based on the experimental protocols of the Ocean Model Intercomparison Project phase 2 (OMIP-2)

“…The higher kinetic energy in FSU-HYCOM can be partially explained by the wind stress formulation which does not take into account the ocean current velocities (absolute winds) while the other three models do (relative winds). The latter has an eddy killing effect that can reduce the total kinetic energy by as much as 30% (see Renault et al, 2019, for a review). This is roughly the difference that is seen between FSU-HYCOM and NCAR-POP and POP with absolute winds in the wind stress (Maltrud and McClean, 2005) has a level of kinetic energy that is close to FSU-HYCOM.…”

“…observations and Chassignet and Xu (2017) argues that one actually needs to significantly increase the resolution (~0.01°) in order to resolve the submesoscale instabilities that can energize the mesoscale (Callies et al, 2016) and therefore enhance eddy kinetic energy comparable to the mesoscale AVISO observations. It is more physical to take into account the vertical shear between atmospheric winds and ocean currents when computing the wind stress (see Renault et al, 2019, for a review) as it allows for a better representation of western boundary current systems (Ma et al, 2016), especially the Agulhas Current retroflection and associated eddies (Renault et al, 2017). In FSU-HYCOM, the Agulhas eddies are too regular and follow the same pathway.…”