Matlab scripts to process sponges and nudging inverse time scales

[arango]

Two new Matlab scripts were added to process sponges and nudging inverse time scales. See ​src:ticket:627 for detailed documentation.

• grid/add_sponge: % Adds enhanced viscosity and diffusion scaling variables (visc_factor and diff_factor) to an existing ROMS Grid NetCDF file. These scales are used in an application to set sponge areas with larger horizontal mixing coefficients for the damping of high frequency noise coming from open boundary conditions or nesting. In ROMS, these scales are used as follows:

     visc2_r(i,j) = visc2_r(i,j) * visc_factor(i,j)
     visc4_r(i,j) = visc4_r(i,j) * visc_factor(i,j)
  
     diff2(i,j,itrc) = diff2(i,j,itrc) * diff_factor(i,j)
     diff4(i,j,itrc) = diff4(i,j,itrc) * diff_factor(i,j)
  

  where the variables visc_factor and diff_factor are defined at RHO-points. Usually, sponges are linearly tapered over several grid points adjacent to the open boundaries. Its positive values linearly increases from the inner to outer edges of the sponge. At the interior of the grid we can values of zero (no mixing) or one (regular mixing).

NOTICE that it is more advantageous to specify these scaling factors in the ROMS Grid that coding it inside ROMS. We can plot and adjust their values in an easy way in Matlab.