$Header$ -*-text-*-

netCDF Operators NCO version 5.2.3 paddle imua

http://nco.sf.net (Homepage, Mailing lists, Help)
http://github.com/nco/nco (Source Code, Issues, Releases)

What's new?
Version 5.2.3 introduces ...
ncclimo now automates the correct options for regional averages
of timeseries of subgridscale fields (useful for ELM/CLM).)
Other fixes to ncclimo splitter behavior are included.
No major new features are implemented.
Skip this release if these changes are not important to you.

Work on NCO 5.2.4 has commenced and aims to add support for Zarr S3 
stores, and to enhance the vertical regridder.

Enjoy,
Charlie

NEW FEATURES (full details always in ChangeLog):

A. ncclimo automatically supports ELM/CLM regional averages.
Previously, ncclimo required non-obvious options to correctly invoke
regional averages of timeseries with sub-gridscale (SGS) fractions,
like surface models often have. Now, when ncclimo is invoked with the
surface model name as the processing type, e.g., ncclimo -P elm ...,
the command internally selects the correct SGS field (landfrac, in
this case) for weighting spatial averages. 
ncclimo -P elm --split -v TBOT -s 1 -e 9 -o $out in*.nc
ncclimo --sgs_frc=landfrac --split -v TBOT -s 1 -e 9 -o $out in*.nc
http://nco.sf.net/nco.html#rgn_avg

B. ncremap's documentation has been updated to include newer weight
generation algotihms and naming conventions. In particular, three
new TempestRemap algorithms are supported and described. Moreover,
the preferred names of about eight algorithms have changed to align
with E3SM conventions. The older names are still supported to ensure
back-compatibility.
ncremap -a ncoaave --map=map.nc in.nc out.nc # New name
ncremap -a esmfaave --map=map.nc in.nc out.nc # New name
ncremap -a esmfbilin --map=map.nc in.nc out.nc # New name
ncremap -a traave --map=map.nc in.nc out.nc # New name
ncremap -a traave --map=map.nc in.nc out.nc # New name
ncremap -a trbilin --map=map.nc in.nc out.nc # New algorithm
ncremap -a trintbilin --map=map.nc in.nc out.nc # New algorithm
ncremap -a trfv2 --map=map.nc in.nc out.nc # New algorithm
http://nco.sf.net/nco.html#alg_typ

BUG FIXES:
   
A. ncclimo fixes an error where it would output, without warning,
unvarying, time-constant timeseries regional averages for ELM.
Those averages are incorrect, and they should vary with time.
There is no workaround. The solution is to upgrade.
Thanks to Sha Feng (PNNL) and Ryan Forsyth (LLNL) for reporting this.

B. ncclimo fixes a recently introduced bug where, when clm_md=hfc
or clm_md=hfs, ncclimo could fail to find input files when run from a 
working directory distinct from the specified input directory.
There is no workaround. The solution is to upgrade.
Thanks to Tony Bartoletti (PNNL) for reporting this.

Full release statement at http://nco.sf.net/ANNOUNCE
    
KNOWN PROBLEMS DUE TO NCO:

This section of ANNOUNCE reports and reminds users of the
existence and severity of known, not yet fixed, problems. 
These problems occur with NCO 5.2.0 built/tested under
MacOS 14.4.1 with netCDF 4.9.3-dev on HDF5 1.14.3 and with
Linux FC38 with netCDF 4.9.2 on HDF5 1.14.1.

A. NOT YET FIXED (NCO problem)
   Correctly read arrays of NC_STRING with embedded delimiters in ncatted arguments

   Demonstration:
   ncatted -D 5 -O -a new_string_att,att_var,c,sng,"list","of","str,ings" ~/nco/data/in_4.nc ~/foo.nc
   ncks -m -C -v att_var ~/foo.nc

   20130724: Verified problem still exists
   TODO nco1102
   Cause: NCO parsing of ncatted arguments is not sophisticated
   enough to handle arrays of NC_STRINGS with embedded delimiters.

B. NOT YET FIXED (NCO problem?)
   ncra/ncrcat (not ncks) hyperslabbing can fail on variables with multiple record dimensions

   Demonstration:
   ncrcat -O -d time,0 ~/nco/data/mrd.nc ~/foo.nc

   20140826: Verified problem still exists
   20140619: Problem reported by rmla
   Cause: Unsure. Maybe ncra.c loop structure not amenable to MRD?
   Workaround: Convert to fixed dimensions then hyperslab

KNOWN PROBLEMS DUE TO BASE LIBRARIES/PROTOCOLS:

A. NOT YET FIXED (netCDF4 or HDF5 problem?)
   Specifying strided hyperslab on large netCDF4 datasets leads
   to slowdown or failure with recent netCDF versions.

   Demonstration with NCO <= 4.4.5:
   time ncks -O -d time,0,,12 ~/ET_2000-01_2001-12.nc ~/foo.nc
   Demonstration with NCL:
   time ncl < ~/nco/data/ncl.ncl   
   20140718: Problem reported by Parker Norton
   20140826: Verified problem still exists
   20140930: Finish NCO workaround for problem
   20190201: Possibly this problem was fixed in netCDF 4.6.2 by https://github.com/Unidata/netcdf-c/pull/1001
   Cause: Slow algorithm in nc_var_gets()?
   Workaround #1: Use NCO 4.4.6 or later (avoids nc_var_gets())
   Workaround #2: Convert file to netCDF3 first, then use stride
   Workaround #3: Compile NCO with netCDF >= 4.6.2

B. NOT YET FIXED (netCDF4 library bug)
   Simultaneously renaming multiple dimensions in netCDF4 file can corrupt output

   Demonstration:
   ncrename -O -d lev,z -d lat,y -d lon,x ~/nco/data/in_grp.nc ~/foo.nc # Completes but produces unreadable file foo.nc
   ncks -v one ~/foo.nc

   20150922: Confirmed problem reported by Isabelle Dast, reported to Unidata
   20150924: Unidata confirmed problem
   20160212: Verified problem still exists in netCDF library
   20160512: Ditto
   20161028: Verified problem still exists with netCDF 4.4.1
   20170323: Verified problem still exists with netCDF 4.4.2-development
   20170323: https://github.com/Unidata/netcdf-c/issues/381
   20171102: Verified problem still exists with netCDF 4.5.1-development
   20171107: https://github.com/Unidata/netcdf-c/issues/597
   20190202: Progress has recently been made in netCDF 4.6.3-development
   More details: http://nco.sf.net/nco.html#ncrename_crd

C. NOT YET FIXED (would require DAP protocol change?)
   Unable to retrieve contents of variables including period '.' in name
   Periods are legal characters in netCDF variable names.
   Metadata are returned successfully, data are not.
   DAP non-transparency: Works locally, fails through DAP server.

   Demonstration:
   ncks -O -C -D 3 -v var_nm.dot -p http://thredds-test.ucar.edu/thredds/dodsC/testdods in.nc # Fails to find variable

   20130724: Verified problem still exists. 
   Stopped testing because inclusion of var_nm.dot broke all test scripts.
   NB: Hard to fix since DAP interprets '.' as structure delimiter in HTTP query string.

   Bug tracking: https://www.unidata.ucar.edu/jira/browse/NCF-47

D. NOT YET FIXED (would require DAP protocol change)
   Correctly read scalar characters over DAP.
   DAP non-transparency: Works locally, fails through DAP server.
   Problem, IMHO, is with DAP definition/protocol

   Demonstration:
   ncks -O -D 1 -H -C -m --md5_dgs -v md5_a -p http://thredds-test.ucar.edu/thredds/dodsC/testdods in.nc

   20120801: Verified problem still exists
   Bug report not filed
   Cause: DAP translates scalar characters into 64-element (this
   dimension is user-configurable, but still...), NUL-terminated
   strings so MD5 agreement fails 

"Sticky" reminders:

A. Reminder that NCO works on most HDF4 and HDF5 datasets, e.g., 
   HDF4: AMSR MERRA MODIS ...
   HDF5: GLAS ICESat Mabel SBUV ...
   HDF-EOS5: AURA HIRDLS OMI ...

B. Pre-built executables for many OS's at:
   http://nco.sf.net#bnr

