WRF connections to GSI

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WRF connections to GSI

• Currently accepts nmm and mass core
• Either binary or netcdf format
• Binary format uses mpi-io
• All grid information contained in wrf files

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WRF connections to GSI
User needs to know how to create a wrf restart
file. GSI not very general yet for
input. Interface is specialized separately for
wrf nmm core and wrf mass core. Plan to add WRF
Lagrangian core eventually and continue to
isolate input-output code for easier adaptation
to other models by interested users.
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WRF connections to GSI

• NMM option
• Input/output on E-grid. For now, no capability
  inside GSI to handle staggered grids.
• Two options
• 1 fill in holes in E-grid
• advantage reduced interpolation error
• disadvantage twice as many grid points
• Use every other row of H variables with no
  interpolation, interpolate V variables every
  other row to saved H points.
• advantage no interpolation of H
  variables, half as many
• points
• disadvantage loss of resolution and
  increased interpolation
• error

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WRF connections to GSI
MASS core option Input/output on B-grid. Only
one option mass variablesno interpolation
wind variablesu interpolated in x to mass
points v
interpolated in y to mass points
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WRF connections to GSI
o g has some interpolation error for both
cases. However this is minimized by
interpolating only the analysis increment back
to the original grid and adding to the input
guess. All interpolations are linear in each
direction.
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WRF connections to GSI
Projection information is not required. The
code automatically determines the local scale
information needed for transforming from global
coordinates to local coordinates, properly
rotating winds to the model frame, and dx, dy
needed for local derivatives (used for psi, chi ?
u,v). All of this is determined from 2-d fields
available on both NMM and MASS core files giving
the earth lat and lon of each model grid point,
and grid dx, dy for every point.
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WRF connections to GSI
Subroutines involved in general earth-to-model
transform (all contained in module
gridmod.f90) init_general_transform using
lats and lons of model grid (converted to
unstaggered analysis grid), initialize various
interpolation and rotation constants, needed for
following routines tll2xy convert earth
longitude, latitude to x,y in grid units
txy2ll reverse of tll2xy
rotate_wind_ll2xy rotate earth u,v to grid
u,v rotate_wind_xy2ll rotate grid u,v to
earth u,v
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WRF connections to GSI
Namelist parameters wrf_ges_filenamefilename
of wrf input restart file. wrf_anl_filenamefi
lename of wrf output restart file. netcdf--
if true, then restart file is in
netcdf format,
otherwise binary format. wrf_nmm_regional if
true, input is from WRF NMM (NCEP)
wrf_mass_regional if true, input is WRF
MASS-core (NCAR) filled_grid, half_grid (for
NMM only) filled_grid if true, fill points
on WRF NMM E-grid
(expensive, but most accurate) half_grid if
true, use every other row of WRF NMM E-grid
(most likely operational
mode)
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WRF connections to GSI
Because NCEP operations will not allow
operational use of netcdf storage format, we have
primarily worked on the binary option, which is
not well developed in the WRF infrastructure. Cur
rently, when running GSI with WRF in netcdf mode,
considerable extra input-output takes place.
Interface routines read/write using WRF library
routines. These create intermediate binary
files, which are read/written by the analysis.
All very clumsy, but workable from user point of
viewthey only need to provide input WRF netcdf
file, and an output WRF netcdf file is created
identical to the input file, but with updated
variables and dates. Problem here is that for
large domains, like the North American window
(order 1000x1000x60 grid points) input-output is
very expensive, especially because not
parallel.
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WRF connections to GSI
In binary mode, the latest version uses mpi-io
and there are no intermediate files. Also, the
input restart file is updated in place, which
means that the user should make a copy of the
input file somewhere upstream of the analysis for
archive purposes and/or to restart in case of
failure. The restart files for the North
American window are currently about 4GB (non-WRF)
and are expected to be even bigger for WRF NAM.
By using mpi-io and only reading/writing the
parts of the file actually needed by the
analysis, substantial time should be
saved.
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WRF connections to GSI
Eventually, we hope to standardize a process so
that users can connect GSI to other models in a
systematic way. Part of this has already been
accomplished by eliminating the need to specify
map projections for the horizontal domain
definition. However support for such activities
will be limited due to the limited resources and
operational focus at NCEP. Continued
improvements in code organization should allow
this possibility for sufficiently motivated
users.