Remote Forcing of the Benguela Current System
Event: 2019 Ocean Surface Topography Science Team Meeting
Session: Science II: Large Scale Ocean Circulation Variability and Change
Presentation type: Type Oral
Contribution: PDF file
We investigate the connections (forces and transports) responsible for variability in the Benguela Current System, one of the major global Eastern Boundary Currents (EBCs). Our focus on this Southeast African current system, a site of economically important fisheries and net absorption of heat by the ocean, is on the seasonal and interannual time scales. As is true of other EBCs, signals from the tropical regions reach the Benguela Current through the wave guide along the western coast of South Africa and comparisons are presented between the Benguela and the EBCs in the Eastern Pacific – the California and Humboldt Current Systems. Previous analyses of these connections have primarily examined sea surface heights from tide gauges and altimetry. Here we include altimeter-derived alongshore velocities and winds, along with transports and water-parcel displacements due to those velocities. Our previous work in the two Pacific systems finds a large difference in the pathways and dynamic systems between the tropics and the EBCs in the northern and southern hemispheres, along with the phasing of the velocity signals in relation to latitude. The pathway in the northern hemisphere is more complex, but the phasing is often such that poleward velocities progress poleward, enhancing the actual poleward displacement of the water parcels as they move to higher latitudes. In the southeast Atlantic, there are similarities to both Pacific systems; 1)The pathway between tropics and mid-latitudes in the SE Atlantic is short and direct, similar to the southeast Pacific; but 2) The pathway in the SE Atlantic is dynamically interrupted by the Angola Dome, similar to the interruptions in the northeast Pacific by the Costa Rica Dome. Perhaps more importantly, the Benguela Current System is directly connected to a Western Boundary Current: the Agulhas Current south of the African continent. Model tracers initiated in the Agulhas system are transported to the Benguela and brought to the surface by upwelling. Thus, we ask three questions: 1) Does the phasing of alongshore transports in the SE Atlantic favor or oppose poleward transport on seasonal and/or interannual time scales? 2) Are inputs from the Agulhas Current System more/less important than inputs from the tropics? and 3) Is local forcing more/less important than the distant forcing? These questions are investigated using a combination of satellite data (altimetry, scatterometry, surface heat fluxes) and model fields.