Ocean bottom pressure signals around Southern Africa from in situ measurements, satellite data, and modeling

Ocean bottom pressure (OBP) variability in the region of the Agulhas Current off the South African coast is a crucial variable in the understanding of dynamic processes in the ocean, but measurements currently available lack either precision or spatial and temporal coverage. We provide a quantitative estimate of OBP variability throughout the region with the help of a setup of the ROMS regional ocean model. Driving the model with boundary conditions from a global ocean model and atmospheric reanalysis data and running it for 8 years, we are able to reproduce many characteristic properties of the regional ocean circulation visible in sea surface height and OBP fields. While the in situ pressure-inverted echo sounders (PIES) measuring local OBP variations on short time scales are sparse in the region, our model provides a comprehensive estimate of OBP variations throughout the region which reach values of up to 15 hPa when barotropic Agulhas rings reach the Cape Basin. These signals turn out to be difficult to measure with current gravimetry solutions from the GRACE satellites, but estimates of localized noise levels for a GRACE follow-on mission let the search for them in future satellite measurements appear viable.