1. Horizontally interpolate ICON fields to medium HOPS grid
   • temperature, salinity & total horizontal velocity.
   • Extend under topography & masks with "Laplacian"-type operator.
   • Set nondimension error field to 0.01 at interpolated points, 1 at extrapolated points with a 2 grid point transition between.
2. Place interpolated ICON fields onto HOPS vertical grid.
   • interpolate temperature & salinity.
   • velocity:
     1. interpolate in vertical.
     2. decompose into baroclinic & barotropic velocities.
     3. solve Poisson equation for transport streamfunction.

The errors introduced in the Poisson solver alone (ie. going from step 2.ii to 2.iii) are illustrated below.