Impact of the current feedback on kinetic energy over the North-East Atlantic from a coupled ocean/atmospheric boundary layer model

Abstract

Abstract. A one-dimensional Atmospheric Boundary Layer (ABL1D) is coupled with the NEMO ocean model and implemented over the Iberian–Biscay–Ireland (IBI) area at 1/36° resolution to investigate the retroactions between the surface currents and the atmosphere, namely the Current FeedBack (CFB) in this region of low mesoscale activity. The ABL1D-NEMO coupled model is forced by a large-scale atmospheric reanalysis (ERA-Interim) and integrated over the period 2016–2017. The mechanisms of eddy kinetic energy damping and ocean upper-layers re-energization are realistically simulated, meaning that the CFB is properly represented by the model. In particular, the dynamical coupling coefficients between the curls of surface stress/wind and current are in agreement with the literature. The effects of CFB on the kinetic energy (KE) are then investigated through a KE budget. We show that the KE decrease induced by the CFB is significant down to 1500 m. Near the surface (0–300 m), most of the KE decrease can be explained by a reduction of the surface wind work by 4 %. At depth (300–2000 m), the CFB induce a reduction of the pressure work (i.e: the PE to KE conversion) associated with a reduction of KE which is significant down to 1500 m. We show that this reduction of KE at depth can be explained by CFB-induced Ekman pumping above eddies that weakens the mesoscale activity and this over the whole water column.

The Copernicus Global 1/12° Oceanic and Sea Ice GLORYS12 Reanalysis

“…The time evolution of the monthly EKE clearly highlights two major discontinuities, which result from changes in the ERAinterim atmospheric forcing in 2002 and in the in situ observing system in 2004. The issue seen in 2002 should be resolved in the next reanalysis version using 1) the new atmospheric reanalysis ERA5, which does not seem to include such variations, and 2) an atmospheric boundary layer model to force the oceanic model (Brivoal et al, 2020;Lemarié et al, 2021). However, further investigations are required to overcome the discontinuity in 2004, resulting from the modification of the 3D-VAR bias correction time window to take into account the increase in the number of in situ T/S vertical profiles due to the arrival of the Argo array.…”

“…Several key developments on the reanalysis system should significantly improve the performance of the next version of GLORYS12. First, the latest versions of NEMO (Madec et al, 2019) will allow to have access to a more coherent Bulk formulation (Brodeau et al, 2017) compared to that used in atmospheric reanalyses, and to the latest wind-current coupling parameterization of Renault et al (2020) and/or to a boundary layer model (Brivoal et al, 2020;Lemarié et al, 2021) dedicated to high resolution ocean coupling atmosphere. In addition, the use of a four-dimensional approach with the data assimilation scheme will also allow an improvement in the spatiotemporal continuity of mesoscale structures, particularly when assimilating SST swath data.…”

A simplified atmospheric boundary layer model for an improved representation of air-sea interactions in eddying oceanic models: implementation and first evaluation in NEMO (4.0)

“…For the sake of consistency, it is preferable to use a bulk formulation as close as possible to the one used to compute the three-dimensional large-scale atmospheric data φ atm LS . Because in the present study the plan is to use a large-scale forcing from ECMWF reanalysis products, we use the IFS (Integrated Forecasting System: https: //www.ecmwf.int/en/forecasts/documentation-and-support/ changes-ecmwf-model/ifs-documentation, last access: 20 January 2021) bulk formulation such as implemented in the AeroBulk (https://brodeau.github.io/aerobulk/, last access: 20 January 2021) package (Brodeau et al, 2017) to compute C D , C θ , and C q in realistic simulations (see Sect. 5).…”