eINALT100 is the central element of the modelling strategy of WHIRLS. It consists of a nested Ocean General Circulation Model configuration that simulates ocean currents and hydrography around Southern Africa at very high resolution. Its horizontal grid at 1/100° (~850 m) resolution and 120 vertical levels covers the Agulhas Current system with the western boundary current (Agulhas Current) along the South African coast, its reflection south of Africa and the shedding of mesoscale eddies transporting heat and salt from the Indian into the Atlantic Ocean. To embed the Agulhas Current system into the global ocean circulation, this child grid, or “nest”, is stacked into a larger basin-scale parent grid at 1/20° which itself is stacked into a global grid at 1/4° resolution.
The main focus of eINALT100 is on simulating submesoscale and mesoscale dynamics. This is well visualized by normalized relative vorticity (𝜁/f, with 𝜁=vx-uy being the relative and f the planetary vorticity), a measure for rotation. Blue (red) colors show anticlockwise (clockwise) motions. Most prominent is the generation of submesoscale motions in austral winter which in particular appear at oceanic fronts and at the edges of mesoscale eddies.
The first 6-year long simulation (2018-2023) of eINALT100 performed on the National High Performance Computing Centre in Göttingen consumed 7.5 million core-hours computing time and marks an important milestone in the development of the WHIRLS model strategy.
The corresponding animation is available at https://oceanrep.geomar.de/id/eprint/62718/
Franziska U. Schwarzkopf and Arne Biastoch, GEOMAR