Page Comparison

This page is under construction...explanation and links will be added in the coming days and weeks...feedback welcome!

ACME model output on unstructured grids is often remapped in a post-processing step to structured lat/lon analysis grids for use by most of our analysis tools.  There  There are numerous problems with these analysis grids employed for remapping by ACME (and CESM) prior to 20150901.  These small flaws or limitations propagate into the weights produced by the weight-generation utility. The flawed weights produce undesirable outcomes (loss of precision, gaps) when converting from source to destination maps. All tested regridders correctly apply the weights they are supplied, and migrating to improved grids (and to mapfiles generated from those grids, e.g., by ESMF_RegridWeightGen or TempestRemap) automatically improves both the numerical accuracy and the data and metadata completeness and consistency of the files produced by the regridding procedure. None of the problems described below affect the accuracy of the model results on the native grid. The affected grids include many FV (plain and staggered) and Gaussian grids known to be used for ACME analysis, mapfiles produced from those grids, and all mapfiles employing bilinear interpolation. The new grids improve the accuracy of diagnostics and the aesthetics of plots produced from regridded files.

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All grids created for this migration thus far are filename date-stamped with 20150901 to facilitate recognizing updated gridfiles and mapfiles. Full creation metadata is in the file header. Any valid netCDF file may be named as the source (e.g., in.nc). It will not be altered. The destination file (foo.nc) will be overwritten. Its contents are immaterial. Add a "-D 7" option to increase the output verbosity and check, e.g., the precision of normalization of area and latitude weights. The API for creating grids is primitive (e.g., having to repeat "--rgr") because it was quickly bolted-on to NCO. We may improve and extend the NCO API to specify other grids and maps in the future. Important updates will be noted here.

Example: 

 We analyzed the global mean net TOA solar radiation for January, 1979 from an ne30 simulation on the native grid and then with old and mapfiles. Tests were performed with commands of the form "ncwa -w area -v FSNT in.nc out.nc" and "ncwa -w gw -v FSNT in.nc out.nc" where in.nc = famipc5_ne30_v0.3_00003.cam.h0.1979-01.nc for the native grid and a regridded version of that for the other mapfiles. The native grid analysis is independent of mapfile and is show for clarity. Analysis grids produced with conservative regridding should exactly reproduce the native grid results. The "area" and "gw" rows show this is only true for the new map with the "–user_area" switch enabled.