(Notes by Philip Cameron-Smith (Unlicensed) based on information from Mark Taylor and Kate Evans (Unlicensed), 2014-10-31 and Steve Goldhaber (Unlicensed) )
(NOTE: this capability has been expanded, and the namelist variables changed, so that old namelists will not work any longer )
The SE dycore runs on cubed-sphere grids (eg, NE30, NE120). The most accurate output is obviously on those native grids. However, plotting and analysis programs often only work with rectangular lat-lon output. And, ACME-CAM may not put all of the necessary information into the output files necessary for general plotting and analysis tools.
ACME is currently working on an interim has a solution that involves a regridding tool that regrids the ACME-CAM output files before reading them into UVCDAT: /wiki/spaces/WORKFLOW/pages/3245930
Another alternative is to tell ACME-CAM to regrid the output onto a rectangular lat-lon grid before writing it out to the output file. This uses bilinear interpolation, which isn't ideal for every purpose, but is good enough for many purposes. . To be safe with this type of interpolation, always interpolate to a grid with finer resolution than the native grid. 25% finer is a good rule of thumb.
This is setup in the user_nl_cam namelist, using the following namelist variables:
interpolateinterpolate_
analysis output =
.
truefalse.,.
truefalse.,.
truefalse.,.
truefalse.,.true.,.true.
interp_gridtype = 1 ! equal angle lat/lon grid, with point at pole (FV scalar grid)
interp_nlat=257 ! for
interpolate_nlon = 0, 0, 0, 0, 0, 128
! Zero means select a resolution close to the native resolution.
! Zero means select a resolution close to the native resolution.interpolate_nlat = 0, 0, 0, 0, 0, 64
interpolate_type = 0, 0, 0, 0, 0, 1
interpolate_gridtype = 0, 0, 0, 0, 1, 2
To regrid a 1 deg atm run, the recommendation from Mark Taylor is to output onto a 0.7 deg grid (ie, 360 degrees / 512 points), slightly finer then the native 1.0 degree:
interp_nlat = 257
! For a true equal angle grid, dimensions should be (N+1) x 2N
interpinterp_
nlonnlon = 512
interpolate_type = 1
! 0 = native high order, 1 = bilinear (default)
This example will cause CAM to output onto a .5 deg grid.interpolate_gridtype = 1
! Equal angle lat/lon grid, with point at pole (FV scalar grid)
The options for the output grid type are:
interpinterpolate_gridtype =
1 equally 1
! Equally spaced, including poles (FV scalars output grid) interp. Use grids of size (N+1) x 2N
interpolate_gridtype =
2 2
! Gauss grid (CAM Eulerian) interp. Use grids of size N x 2N
interpolate_gridtype =
3 equally 3
! Equally spaced, no poles (FV staggered velocity) Not Recommended
The interpolate_analysis options are for the different history tapes.
In the code there appears to also be There is also an option for the type of regridding:
interpinterpolate_type =
1 0
! 0 0 = native high order, 1
interpolate_type = 1
! 1 = bilinear (default)
is included in Notes on tuning 1 degree ACME v0 model
(Note: This regridding capabalitiy is included in /wiki/spaces/SIM/pages/7995515)