Gemclim 3.3.3.1 nudging

Spectral nudging

Grid size restrictions

To be able to use spectral nudging in CRCM5, the core grid needs to match the FFT criteria in x- and y-direction. You can use 'findfft' to find get the possible values for 'Grd_ni' and 'Grd_nj' in your gemclim_settings.nml.
For example:

    findfft -gnimax 500 -cfl Pil_maxcfl

Put the value of 'Pil_maxcfl' from your gemclim_settings.nml!
Your 'Grd_ni' and 'Grd_nj' will then have to be one of the values findfft spits out.
If your grid is larger than 500 points, just set '-gnimax' to a number large enough for you.

  Lam_spn_half_respon = 1000.  ,
  Lam_spn_nudging_S = 'UV'     ,

Controlling the profile

There are 3 parameters for this:

    Lam_spn_up_const_lev : above this level (in hybrid values) the profile is set to 1 (default 0.).

    Lam_spn_start_lev : below this level (in hybrid values) the profile is set to 0 (default 1.).

Between these two, the profile goes from 0 to 1 either linearly or with a cos2 function. This can be set with the third parameter:

    Lam_spn_trans_shape_S = 'LINEAR' : profile changes linearly (default)
    Lam_spn_trans_shape_S = 'COS2' : profile changes with cos2 function

So you will want to put:

    Lam_spn_up_const_lev  = 0.       ,
    Lam_spn_start_lev     = 0.5      ,
    Lam_spn_trans_shape_S = 'LINEAR' ,