relax/README.relax:

Interpolation of climatology to a HYCOM model grid for use in boundary
relaxation zones or for model initialization.

../ALL/bin/clim_stat	lists contents of "native" climatology
../ALL/bin/clim_stat.1	man page for clim_stat
relax/010/		"isopycnal" climatology for a HYCOM simulation
relax/999/		zonal isopycnal depth climatology for HYCOM poflat
relax/levitus/		Levitus climatology on HYCOM horizontal grid
relax/plot/		plot climatology
../ALL/relax/src/ 	softlink to latest source directory

See also:

relax/plot/README.relax.plot
ALL/relax/src/README.relax.src
999/README.relax.zonal

The climatology data sets are input on their native grid, from standard
Naval Research Laboratory (NRL) climatology files.  The ../bin/clim_stat
command lists the contents of a native climatology file.  All fields must be
defined at all grid points (including over land and below the ocean floor),
and the potential density vertical profile must be stable at all locations.
Levitus in the required format is available from the HYCOM ftp site, see:
ftp://obelix.rsmas.miami.edu/awall/hycom/levitus_for_hycom.tar.gz

First interpolate (Levitus) climatology to the HYCOM horizontal grid, but
keeping the original z-grid in the vertical (see relax/levitus).  The
interpolated climatology is defined at all grid points (including land and
below the ocean floor), and its potential density vertical profile is stable
at all locations.  Levitus is defined using Sigma0, but the interpolated
climatology can be Sigma0, or Sigma2, or Sigma4.  

Then convert to the "isopycnal" climatology required for a particular HYCOM
simulation (see relax/010/relax.com).  The region and simulation specific 
environment variables are in relax/010/EXPT.src.  The required input file,
relax/010/blkdat.input, can be created from expt_01.0/blkdat.input using 
the script relax/010/blkdat.com.  The output data sets are climatological
interface depth, potential temperature and salinity fields for the specified
set of isopycnal layers and the specified set of minimum near-surface layer
thicknesses.  The result can be plotted using the standard HYCOM archive
file plot program, see relax/plot.

Splitting the process into two phases saves time, because the z-level
climatology does not depend on the isopycnals chosen by a particular HYCOM
simulation.  Also conversion to isopycnals does not depend on which
climatology is being used (providing all the native climatologies use the
same number of z-levels in the vertical).

A 2-D relaxation mask is also required for any HYCOM simulation that uses
lateral boundary nudging.  It is typically zero everywhere except the 
boundary regions where relaxation is to be applied.  In the boundary 
regions it is the relaxation scale factor (1/seconds).  The program 
src/rmu.f can be used to specify the boundary relaxation zones, see 
relax/010/relax_rmu.com.  Input is up to 99 individual patches and the 
associated e-folding time in days (which is converted internally to 
1/e-folding-time-in-seconds for assignment to rmu). 

HYCOM 2.0 uses the array (.a) and header (.b) file format, and a 
vertical mapping from z-levels to isopycnals that is based on Rainer
Bleck's "restep" proceedure for converting one stairstep (i.e., 
piecewise constant) set of profiles (in this case between z-levels) 
into another with prescribed density steps.  This is augmented by a 
simplifed hybgen proceedure to map the resulting isopycnals to hybrid 
layers.

HYCOM 1.0 used the pakk file format, and a different vertical mapping 
from z-levels to hybrid layers.