The impact of resolution on the air-sea interaction in the Agulhas current region

Sea surface temperature (SST) has been thought to be linked with air-sea surface heat fluxes (SHF). General knowledge is that the high frequency variating atmosphere properties modify oceanic quantities due to their slower response. However, recent studies show how in regions where SST gradients and heat losses are stronger – in the Western Boundary Currents region (WBC) – variabilities in SST and SHF are due to internal ocean processes and water dynamic effects. Theoretical models suggest that the correlation between SST and SHF and between SST tendency (namely the time derivative) and THF can be used to retrieve the sources of variations of these two quantities distinguishing to influences due to ocean or atmosphere dynamics (ocean or atmosphere driven regimes). In this study, We use observational data and numerical model outputs with different resolutions to distinguish different regimes of variability and to investigate spatial resolution effects over the Agulhas Current region and the Eastern South Atlantic. In these regions waters flowing southward from the Indian Ocean along the eastern coasts of Africa interact with bathymetry and cold waters of the Antarctic Circumpolar Current (ACC) and the SubTropical Front and generate turbulence and eddies that propagates into the South Atlantic carrying warm and salty waters (Agulhas Leakage). Hence this methodology is particularly effective due to the mesoscale length scale of the physical phenomena that occur here. Observations are retrieved from OAFlux dataset and J-OFURO3. Model data come from the Coupled Model Intercomparison Project (CMIP6). The increase of ocean resolution leads to a better representation of the cross-covariance patterns and cross-correlation forms, indicating an improvement of the eddy-permitting from the eddy-parametrized models’ capability. Covariance maps have been calculated to highlight qualitative patterns for the lead-lag symmetry. We concluded that, while high resolution model data have similar covariance patterns and correlation values to the observations, their low-resolution counterpart, in two cases, fails to reconstruct the signal caused by the ocean dynamics. The stronger impact on the capability of reproduce this interaction phenomenon belongs to the ocean part of the coupled model: the higher, the better is the symmetric properties of the correlation functions (symmetry index) and the greater the transition scale is, implying the needs of a wider filtering window to cancel out the ocean driven regime signal.