NetCDF operators (NCO) version 5.1.2

Version 5.1.2 of the netCDF Operators (NCO) has been released. NCO is an Open Source package that consists of a dozen standalone, command-line programs that take netCDF files as input, then operate (e.g., derive new data, average, print, hyperslab, manipulate metadata) and output the results to screen or files in text, binary, or netCDF formats.

The NCO project is coordinated by Professor Charlie Zender of the Department of Earth System Science, University of California, Irvine. More information about the project, along with binary and source downloads, are available on the SourceForge project page.

From the release message:

Version 5.1.2 improves support for horizontal regridding, vertical interpolation, or both, on ultra high-resolution model output. Users of such functionality may benefit from upgrading, otherwise this release can be skipped.

New Features
  1. ncremap supports new options and --ps_nm=ps_nm. The argument to --vrt_in is a vertical coordinate file that contains the pure or hybrid pressure information for the input data to be vertically interpolated. Previously, this information was required to be present in the input data file. However, SCREAM/EAMxx and other ultra-high resolution models may choose to output the grid information in separate files from the geophysical fields. This can save considerable space, especially for hybrid sigma-pressure coordinates with time-varying surface pressure. To complement the --vrt_in option, there is now a --vrt_out option to explicitly identify the file containing the output vertical grid. The best practice is now to use --vrt_out (instead of --vrt or --vrt_fl, which still work) to specify the output vertical grid and clearly distinguish it from the input vertical grid, if any.
    ncremap # Output vertical grid option new name
    ncremap ... # Specify both grids
  2. Previously the vertical interpolation feature required that the surface pressure field for hybrid coordinates be named PS. Now the name of the surface pressure field can be changed using the convenient ps_nm option. Moreover, if the argument of --ps_nm includes a filepath separator (slash or backslash), then the portion preceding the final separator will be treated as a filename path, and the final portion will be treated as the surface pressure variable name:
    ncremap --ps_nm=ps ... # Surface pressure is ps not PS
    ncremap --ps_nm=/path/to/ ... # Use ps from
  3. ncclimo and ncremap support a new procedure type option, -P eamxx. This option automatically generates ncremap flags useful for E3SM EAMxx datasets. In addition to their typically ginormous size, these datasets have different dimension and variable names than EAM/CAM. Current -P eamxx causes ncremap to do two actions automatically: (1) Permute the horizontal dimensions to be most rapidly varying by generating the option --pdq_opt=ilev,lev,dim2,col prior to horizontal regridding. (2) Search for surface pressure under the name ps instead of PS prior to vertical interpolation of hybrid-pressure grids.
    ncremap --pdq_opt=ilev,lev,dim2,col # Manual dimension permutation
    ncremap --ps_nm=ps # Manual surface pressure renaming from PS to ps
    ncremap -P eamxx # Both options automagically
  4. ncremap has changed the default behavior of outputting the staggered grid to finite volume (FV) destination grids from opt-out to opt-in. This means that it is no longer necessary to specify --no_stg_grd when regridding. Instead, it is necessary to specify --stg_grd when the staggered grid (including variables slat and slon) is desired as additional information in the regridded file.
    ncremap --no_stg_grd ... # Old method of opting out
    ncremap ... # New default behavior
    ncremap --stg_grd ... # Recovers old default behavior
  5. ncremap vertical interpolation routines now recognize variables with names T_mid and VerticalLayerMidpoint as containing temperature and geopotential height, respectively. These variable names are used in SCREAM/EAMxx. The default extrapolation for these variables now behaves the same as T and Z3 for EAM/CAM datasets.
  6. ncz2psx now has a man page. Full documentation for ncz2psx is expected to become available once NCO fully supports the Amazon S3 scheme for NCZarr in 2023.

Additional details are available in the ChangeLog.


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