(Notes by Philip Cameron-Smith (Unlicensed) based on information from Mark Taylor and Kate Evans (Unlicensed), 2014-10-31)
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 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:
interpolate_analysis = .true.,.true.,.true.,.true.,.true.,.true. ! native grid or interpolation can be different for each history file
interp_gridtype = 1 ! equal angle lat/lon grid, with point at pole (FV scalar grid)
interp_nlat=257 ! for a true equal angle grid, dimensions should be (N+1) x 2N
interp_nlon=512
This example will cause CAM to output onto a 0.7 deg grid (360 degrees / 512 points), slightly finer then the native 1.0 degree, as recommended.
The options for the output grid type are:
interp_gridtype = 1 equally spaced, including poles (FV scalars output grid). Use grids of size (N+1) x 2N
interp_gridtype = 2 Gauss grid (CAM Eulerian). Use grids of size N x 2N
interp_gridtype = 3 equally spaced, no poles (FV staggered velocity) Not Recommended
The interpolate_analysis options are for the different history tapes. It is a vector with 8 elements: seven different history files, plus inithist, which is the last one and should always be on the native grid.
In the code there appears to also be an option for the type of regridding (but I haven't tested it):
interp_type = 1 ! 0 = native high order, 1 = bilinear (default)
(Note: This regridding capabalitiy is included in Notes on tuning 1 degree ACME v0 model)