Overflow regions in ocean

File:  /models/ocn/pop2/input_templates/gx1v6_overflow

Contact the Gokhan Danabasoglu  (gokhan@ucar.edu) in the NCAR ocean model group for details on the physical implications of the overflow process.

Hardcoded modern ocean physical conditions

Banda Sea, Tidal mixing levels, Ross Sea, overflow locations, anisotropic horizontal viscoscities and enhancement along the western boundaries of the oceans

-The spatial variability of the background diffusivities for
the vertical mixing scheme has latitudinal dependence (e.g., Banda

So, setting the logical you
mention below should turn this off. I think you already know
about the anisotropic horizontal viscosities and enhancement
along the western boundaries of the oceans. ... and the overflow
locations are also grid dependent.

 vmix_kpp.F90, the backround diffusitivites are
 hardwired for the specific lat/lon areas bounding the
 modern world Banda Sea...

although, this code is only used when
set lhoriz_varying_bckgrnd is set to true... and therefore,
not relevent for deep time, as we set this parameter
to "false".

Turning off overflows:

pop2.buildnml.csh - set overflows_on = .false.

alternatively, keep overflows on for diagnostic output, but not prognostic:

   overflows_interactive  = .false.

   overflows_on           = .true.
   overflows_interactive  = .true.
   overflows_infile       = '$overflow_filename'
   overflows_diag_outfile = '${output_d}o'
   overflows_restart_type = 'ccsm_$runtype'
   overflows_restfile     = '${output_r}o'

Branching from a run with overflows turned ON

The overflow code has to modify the original startup ocean kmt bottom topography to run. These kmt changes
are saved in the restart file as changes to the computational domain. On restart, the kmt field is
modified as originally during startup, so it is consistent
with the restart file. Our experience is that if one
does a restart using a file that originally had overflows,
but now you change the namelist input file to turn them
off, pop may not be stable.

tidal mixing:

Tidal mixing is geography dependent and is closely tied to the present day.  We have

tidal_mixing = .false.

  ltidal_mixing          = .true.
  local_mixing_fraction  = 0.33
  mixing_efficiency      = 0.2
  vertical_decay_scale   = 500.0e02
  tidal_mix_max          = 100.0
  tidal_energy_file      = '$tidal_mixing_filename'
  tidal_energy_file_fmt  = 'bin'