A Trailblazing Global Ocean Simulation in the Time of Wide Swath Altimetry

We present the development of a next-generation family of Lat–Lon–Cap (LLC) global ocean simulations, culminating in LLC8640, a 1/96^◦ (≈ 1 km) realistic global 'nature run’ that, once complete, will represent the highest-resolution global ocean model produced under realistic conditions. This effort advances well beyond the widely used LLC4320 configuration by addressing long-standing dynamical biases through coordinated improvements in resolution, physical formulation, and forcing.

Key advances include increased vertical and horizontal resolution, updated global bathymetry, non-linear free surface, explicit ice-shelf cavities around Greenland and Antarctica, hourly atmospheric forcing, realistic river discharge, and improved astronomical tidal forcing. Together, these developments directly target deficiencies in earlier LLC models, including a misplaced Gulf Stream, a crude representation of Antarctic shelf circulation, and weak tropical instability waves. Particular emphasis is placed on the equatorial ocean, where Green’s-function-based approaches are used to optimize turbulence parameterizations and reduce persistent discrepancies between global models and observations. Early results from the ongoing lower-resolution spin-up already demonstrate markedly improved realism, including a more accurate Gulf Stream path and a strengthened, more realistic equatorial undercurrent.

The modeling strategy employs a staged spin-up across resolutions: a multi-year 1/12^◦ (LLC1080 ) integration to equilibrate large-scale circulation and kinetic energy; a subsequent 1/48^◦ (LLC4320 ) phase to sharpen mesoscale and submesoscale dynamics; and a final month-long 1/96^◦ (LLC8640 ) integration producing several petabytes of hourly three-dimensional velocity, temperature, and salinity fields. The resulting dataset will provide an unprecedented global benchmark for studies of internal tides and waves, submesoscale turbulence and mixing parameterizations, and SWOT-era sea-surface height variability.