Nesting a nonhydrostatic model in a hydrostatic model: The boundary interface

► Submesoscale nonhydrostatic hindcast is forced with forecasted hydrostatic open BCs. ► Hydrostatic baroclinic velocities are adjusted after interpolation to the inner grid. ► Adjustments explicitly enforce volume conservation of the open BCs. ► A relaxation scheme matches values across the periphery of the submesoscale domain. ► Discontinuities, reflections and perimeter currents at the periphery are prevented.